DEEP-WATER BRACHYURAN CRABS OF THE STRAITS OF FLORIDA (CRUSTACEA, DECAPODA)

Trabajo recibido el 8 de septiembre de 1983 y aceptado para su publicación el 31 de enero de 1984.

RESUMEN

INTRODUCCIÓN

Our present knowledge of the deep-water brachyuran crabs inhabiting the Straits of Florida has greatly benefited from the extensive work in the field of systematics that followed the early oceanographic expeditions conducted in the area, namely those of the BACHE, BLAKE, ALBATROSS and FISH HAWK . These expeditions provided rich material for the now classic works on brachyurans published by Stimpson (1881), Milne Edwards (1880), Milne Edwards and Bouvier (1902; 1923), and Rathbun (1918, 1925, 1930, 1937). Similarly, the deep-water collection made by the R/V ATLANTIS off the coasts of Cuba (Chace, 1940), have contributed to the addition of undescribed forms of brachyurans and to the clarification of the taxonomic status of several species that occur in the Straits. Additional information on the composition of the deepwater crabs of the Straits can partially be derived from the list of brachyuran species given by Thompson (1985) based on the collections made by the exploratory fishing vessels OREGON and COMBAT.

The records provided by Pequegnat (1970) of the deep-water brachyurans obtained by the R/V ALAMINOS in the Gulf of México are of particular relevance to the present study, because of the close geographic proximity of this area to the Straits of Florida. These records have specially served the purpose of bringing up to date the bathymetric and geographic distribution of 36 taxa, 27 of which are normal inhabitant of the Straits.

The present study documents the horizontal and vertical dispersion of each faunal component as related to environmental factors such as temperature, depth and substrate.

The material reported upon here was collected by the R/V GERDA in the area of the Straits of Florida, as part of the Deep-Sea Biology Program of the Rosenstiel School of Marine and Atmospheric Science (RSMAS), University of Miami. The program was initiated in May of 1962 and ended ten years later. During this period of time, both benthic and mesopelagic faunas of the Straits were thoroughly sampled with the aid of otter trawls, dredges, Isaacs-Kidd midwater trawls (IKMT), and plankton nets. A detailed account of the gear employed and its operation was given by Devany (1969) and Staiger (1970).

The total number of stations logged by the R/V GERDA amounted to 1348 of which 477 correspond to bottom stations made in waters in excess of 100 fm (183 m). Brachyuran crabs were obtained in 273 of these stations which yielded 1888 specimens, representing 87 species and 18 families. To add accuracy in the interpretation of the vertical dispersion of these species, material collected by means of plankton nets, IKMT, or that had unreliable depth records were not considered in the present study. Owing to these circumstances, 24 of the original 297 GERDA stations were eliminated. The majority of the brachyurans included herein were collected with a ten-foot (3 m) otter trawl which seems to provide a good qualitative sample of the dominant species that could be captured in greater numbers should a trawl of larger dimensions be used. The appropriate specifications on the construction of the ten-foot trawl are offered by Staiger (1970).

The identifications process was mainly carried out at the RSMAS Invertebrate Museum and the Rijksmuseum van Natuurlijke Historie of Leiden, The Netherlands. Further consultation work was conducted at the Museum National d'Histoire Naturelle in Paris, and the British Museum (Natural History) in London. This phase of the study relied heavily on the four comprehensive monographs on the recent crabs of the western hemisphere written by Mary J. Rathbun, (1918, 1925, 1930, 1937). They are often cited in the description references unless additional citations were pertinent to clarify the synonymy of some of the taxa studied. Other useful sources of reference were the excellent descriptions given by Milne Edwards and Bouvier (1880, 1902, 1923) contained in the BLAKE reports, Chace's (1940) paper on the brachyurans taken by theATLANTIS, Williams' (1965) thorough account of the decapod fauna of North Carolina, and the various papers published by Guinot-Dumortier (1959, 1960, 1966, 1967, 1969). While this paper was being prepared, two of the taxa contained in it were described as new species by Williams (1974) and Türkay (1975). The first instance was that of the small xanthid crab Allactaea lithostrota hitherto known from off North Carolina; the second was the grapsid crab Euchirograpsus antillensis whose paratypes include specimens recovered by the GERDA in the Straits.

The species composition at each GERDA station was obtained from the computer program SORTSP prepared by Miss Ivonne Brommfield for this purpose. Subsequently, the frequency of occurrence and relative abundance were determined for each taxa, and the appropriate ranking tables were then constructed (Tables 1 and 2). Data from these tables were later employed to illustrate the position of individual species, in terms of the percentage frequency of occurrence and abundance, within the entire brachyuran collection. The method selected to present this information was the so called QuadrantGraph successfully utilized by Ono (1961) in his ecological study of the brachyuran community of Tomioka Bay, Japan. The method consists in plotting the percentage frequency of occurrence of each taxa on the ordenate, and the tabulated mean number of individuals per sample on the abscissa. The graph is divided into four quadrants (Fig. 1) by the corresponding mean values of frequency and abundance, and their 95 % confidence limits (2.68 <=3.5 <= 4.3; 2.08 <= 2.7<=3.4). The numbers appearing in each quadrant, represent the number given for species in Table 1. The quadrant I enclosed the dominant species of brachyurans which were frequent and abundant in the GERDA collection. Quadrant II comprises the elements which occured in large numbers but rather infrequently. Quadrant II includes the occasional elements represented by a limited number of individuals. Finally, Quadrant IV comprises the common species often recovered by the GERDA but always in reduced numbers. (Fig. 1.)

TABLE 1 RANKING OF SPECIES BY FREQUENCY TO OCCURENCE IN THE GERDA COLLECTION

TABLE 2 RANKING OF SPECIES BY FRECUENCY OF RELATIVE ABUNDANCE IN THE GERDA COLLECTION

As a convenient way to gain insight into the actual spacing pattern of the individuals sampled, the coefficient of dispersion (CD) was computed for the taxa with more than six single occurrences. The values of the coefficient were obtained by calculating the ratio between the variance of the species' numerical distribution and its mean number of specimens (CD = S² x). Ratio values will tend to unity if the individuals of the given species are randomly dispersed (Poisson distribution), to less than unity if they happen to be over dispersed, and to more than unity when they are aggregated. The significance of the departure from unity is usually tested by the formula:

where is the total number of samples (i.e. 273). The estimated significance level for the total samples was 0. 169 ± 1. This coefficient of dispersion has effectively been employed in studies of both benthic and mesopelagic populations (Gage and Geekie, 1973; Jumar, 1975; Pearcy, 1964; Ebeling et al., 1970) to scan the data for obvious cases of strong aggregation of individuals within species.

For the sake of future comparative work, the same map of the Straits utilized earlier by Staiger (1970) has been adopted in the distributional analysis of the deep brachyuran fauna of this area. A series of distributional plots indicating the position of the GERDA stations were generated for each species with the combined use of an appropriate program, available at RSMAS, and a CALCOMP 563 plotter. Similarly, in the description of these distributional maps the three topographic units first suggested by Wennekens (1959) and Devany (1969) were retained: southern, central, and northern Straits (Fig. 2). For the purpose of interpreting the effect that the hydrographical conditions exert upon the dispersion of the brachyuran crabs, this study made use of the information on water mass properties of the Straits given by Wennekens (1959), the isothermal profiles drawn by Clausner (1967), and the summary of such conditions later offered by Devany (1969). Much of the data concerning the major geological features of the Straits were derived from a series of important contributions covering the subjects of geomorphology, bathymetry, and sediment distribution of the area (Gorsline, 1963; Gorsline and Milligan, 1963; Hurley et al., 1962; Hurley and Fink, 1963; Jordan et al., 1964; Malloy and Hurley, 1970). Specific information on the type of substrate observed at a given location, was obtained from the GERDA's deck log.

Fig. 1. Quadrant-Graph

No descriptions of species are included in this paper. Reference is made to the best descriptions available of the deep-water brachyurans occurring in the area of study. Under geographic range is given the source of the most significant reports of each species. The bathymetric range refers to the least and greatest depth range in meters recorded for the species.

Reference to the material examined has been designated as follows: the initial G stands for the R/V GERDA, which is followed by the station number; the next digits accompanied by a letter indicate the number and sex of the specimens identified; f,for the females; m, for the males andj, for juveniles. Listing of the GERDA stations is available from the author.

Fig. 2. Topographic units of the Straits of Florida

Lyreidus bairdii Smith, 1881

Description. Rathbun, 1937, p. 23, pl. 5, figs. 5-6.

Geographic range. Western Atlantic from Massachusetts to Puerto Rico; Gulf of Mexico; Greater Antilles; Panama, off Punta Brava.

Bathymetric range.119 to 824 m.

Material examined. G-173, 3 f, 6 m; G-657, 21 f, 16 m; G-21, 3 j; G-172, 15 j; G-174, 3 m, 1 f; G-462, 1 m.

Distribution analysis. L. bairdii is a species which occured rather infrequently throughout the GERDA collection but, when captured, a large number of individuals were recovered (Fig. 1). A total of 69 specimens of this raninid were identified, ranking 7th among the ten most abundant elements included in the present study. The males were predominant over the females by a ratio of 2: 1.

L. bairdii shows a well defined distributional pattern restricted to the continental side of the Straits. Most of its records were recovered from the edge of the continental shelf of the northern Straits off the St. Lucie Inlet (Fig. 3). Two additional records were taken off Miami and Dry Tortugas, respectively. The coefficient of dispersion of this species (CD = 24) exceeded by a large magnitud the computed level of significance expected for a random distribution, thus suggesting a strong aggregative spatial dispersion.

The vertical distribution of L. bairdii in the Straits has a very limited range from 180 to 210 m with an average depth of 195 m.

Remarks.This raninid has been reported from areas adjacent to the Straits but usually at greater depths than above. Pequegnat (1970) extended its bathymetric range in the Gulf of México down to 450 fm (824 m); however, in accordance with the population density values given by this author, the species attains its peak abundance between 211 and 275 m. The insular dispersion of L. bairdii near Puerto Rico and the northern coast of Cuba seems to be confined to depths ranging from 430 to 549 m, (Rathbun, 1937; Chace, 1940). From the collections of the COMBAT and the PELICAN, Bullis and Thompson (1965) listed this species as ocurring on the outer shelf off Cape Cañaveral.

Ecological note.Substrate and depth are the two main factors that seem to govern both the horizontal and vertical dispersion of L. bairdii in the Straits. Substrate data were available for three of the six station in which this crab was secured by the GERDA. One station indicated a mud/shell rubble bottom, another indicated soft mud ooze, and yet another mud/test fragments.L. bairdii is a well adapted burrowing form whose substrate preferences are limited to the smooth mud bottoms known to occur throughout the continental margin of the Florida side of the Straits, (Hurley and Fink, 1963; Staiger, 1970). The apparent discontinuity observed in the distribution of this species along the Pourtales Terrace (Fig. 3) is presumably a reflection of its substrate requirements; bottoms in the Terrace are known to be predominantly rocky and rather rough, covered with calcareous debris of corals, echinoderms and mollusks. It is, therefore, justifiable to assume that this circumstance coupled with the restrictive depth range exhibited by the species could prevent its establishment on the insular side of the Straits.

Geographic range. Straits of Florida; Cuba; Gulf of México; Caribbean Sea, east of Isla Margarita, Venezuela.

Bathymetric range. 47 to 392 m.

Material examined. G-722, 1 f; G-982, 1 m; G-985, 10 j.

Distribution analysis.In spite of the few occurrences of R. constricta in the Straits, this raninid crab appears among the characteristic species in view of the large number of juvenile specimens taken from a single haul; such a number accounts for the relatively high average value of individuals per sample computed for the species (Fig. 1).

Fig. 3. Distributional pattern of Lyreidus bairdii collected by the GERDA

R. constricta is distributed on the insular central sectors of the Straits. One of the records was obtained at 392 m near the mounth of the Northwest Providence Channel, and the two other were taken at the northwestern end of Cay Sal Bank at depths of 201 and 210 m. The first record represents the maximum depth range for the species.

Remarks. R. constricta exhibits a rather patchy distribution throughout the West Indian region; prior to this study, the species was only known from the inner shelf of Sombrero reef, Florida (Milne Edwards, 1880), and from Bahia Honda, Cuba (Rathbun, 1937). More recently, Pequegnat (1970) reported this species from the upper continental slope of the south eastern Gulf of México; based on this finding, Pequegnat suggested the possibility that R. constricta may also be found in the Western Caribbean. My own examination of the brachyuran collection obtained by the R/V PILLSBURY in the Caribbean region revealed a single male specimen of this raninid crab identified by Dr. L. B. Holthuis (unpublished); this record was taken from a locality east of Isla Margarita, Venezuela, at a depth of 47 m (PILLSBURY station 710, 10°47'N, 62°55'W).

Description.Rathbun, 1937, p. 13, text-fig. 8, pl. 1, figs. 3-4.

Geographic range. Straits of Florida; north coast of Cuba; Greater Antilles to Panama.

Bathymetric range. 20 to 366 m.

Material examined. G-537, 2 m; G-876, 1 m; G-725, I f, 1 ovigerous f; G-681, 1 m; G-982, 1 ovigerous f; G683, 1 m; G-624, 3 f, 2 m; G-394, 4 m.

Distributional analysis. R. lamarcki represents one of the common species of brachyurans in the Straits whose frequency rank of occurrence (25th) nearly equals that of its abundance (22). A total of 17 specimens was identified with the males predominating over the females by a 2:1 ratio; only two gravid females were obtained. The numerical distribution of individuals in the eight GERDA stations was almost homogeneous except for two isolated instances in which more than four individuals occurred in a single sample. This fact is perhaps reflected on the S²/x ratio for the species (CD = 3) which does not notably depart from the significant level for a random distribution.

R. lamarcki is essentially an insular species whose pattern of distribution closely follows the 100 fm contour (183 m). Records for this species were obtained from the northern end of Cay Sal Bank, the northwestern side of the Great Bahama Bank, off Bimini, and the Great Isaac Light; and from the Northwest Providence Channel near the Berry Islands; one single record was taken at the northwestern side of the Little Bahama Bank (Fig. 4).

The depth interval obtained by placing 95 % confidence limits on the mean depth of occurrence of R. lamarcki (189 <= 216 <= 242 m), corroborates its restricted bathymetric range.

Remarks. The records given here for R. lamarki have extended its northern geographic range into the Straits as far north as the western corner of the Little Bahama Bank. Chase (1940) had previously reported this species from three ATLANTIS stations off the northern coast of Cuba and the Old Bahama Channel. Further reports for the species have been offered by Bayer et al. (1970) in their study of the benthic Panamic biota. According to this study, R. lamarcki is a frequent brachyuran element of the shelffauna taken at depths as shallow as 20 m, by using the recurrent group analysis (Fager and Longhurst, 1968) the above authors were able to recognize this raninid as a component of the so-called MUD-SPONGE community that occurs on the Caribbean side of the Panama Canal. The number of records given in the referred study far outnumbered any previous collection of R. lamarcki.

Ecological note.Substrate information for R. lamarcki was limited to two localities out of the ten in which this species was captured. The first locality indicated the existence of a calcareous/Halimedabottom, and a second one indicated hard substrate. In the Straits, the maximum depth of dispersion of this species nealy coincides with the 18°C isothermal profile (Devany, 1969). This circumstance may be indicative of the thermal tolerance of this element, which does not seem to withstand temperatures colder than 18°C; the same temperature restriction applies to one of the records obtained by the ATLANTIS in the northern coast of Cuba off Bahia Matanzas (Chace, 1940). In this particular instance, Chace recorded three individuals captured at approximately 307 m. from a locality bounded by the referred isotherm. As a result of the extreme compression of the isotherms on the continental side of the Straits, the intersection of the 18° profile always takes place above the 200 m mark. This condition could discourage the settling of R. lamarcki in biotopes that fall outside the boundaries of the continental shelf proper.

Homolodromia paradoxa A. Milne Edwards, 1880

Description. Rathbun, 1937, p. 58, pl. 13, figs. 1-3, pl. 14, figs. 14.

Geographic range.Straits of Florida; north coast of Cuba; Caribbean Sea, and Leeward Islands.

Bathymetric range. 577 to 897 m.

Material examined. G-190, 1 f, 1 m; G-289, 1 f; G918, 1 f; G-918, 1f, 1 m.

Distributional analysis. H.paradoxa is a truly deep-water crab captured occasionally by the GERDA. Only five specimens were taken from two widely separated localites, and, interestingly enough, in one such locality pairs of females and males co-occurred twice in separate hauls; earlier reports of the species (Milne Edwards, 1880; Chace, 1940) had only yielded male individuals.

Fig. 4. Distributional pattern of Raninoides lamarcki collected by the GERDA

H. paradoxawas found distributed off the Pourtales Terrace at a depth of 577 m and in the Northwest Providence Channel west of the Berry Islands at a depth of 814 m.

Remarks. The present findings extend the geographical range of H. paradoxa northward into the Straits of Florida and the Bahamas area; its former northern limit was the north coast of Cuba (Chace, 1940).

Homola barbata (Fabricius, 1793)

Description. Thelxiope barbata, Rathbun, 1937, p. 63, text-fig. 16, pl. 15, figs. 12. Homola barbata, Williams, 1965, P. 146, fig. 121.

Geographic range. Off southern Massachusetts to the Caribbean Sea; Eastern Atlantic from Portugal and Azores to Madeira Islands; Mediterranean Sea; South Africa.

Bathymetric range. 55 to 683 m.

Material examined. G-678, 1 m; G-533, 1 f; G-1125, 1 f; G-1312, 1 f; G-706, 1 f; G-679, 1 f; G-681, I m; G-626, I f, 1 m; G-134, 1 m; G-135, 1 m, 1 ovigerous f; G-168, 1 j; G-233, 1 f; G-387, 1 f, 1 m; G-482, 1 f, 1 m; G-510, 1 f; G-493, 2 j.

Distributional analysis. H. barbata is a rather common element of the brachyuran fauna of the Straits, ranked 10th by its frequency of occurrence though seldom more than two individuals were taken at each haul; this explains its inclusion in quadrant IV of figure 1.

A total of 20 specimens was identified, the females slightly predominant over the males; only one ovigerous specimen was recorded from the Pourtales Terrace. According to the index of dispersion computed for this homolid (CD = 1-4), its spatial dispersion approximates the level of significance expected for a random distribution.

The distributional pattern of H. barbata is essentially confined to the insular margin of the Straits, although there is evidence that confirms the presence of this crab on the continental side as well. In the present study, two isolated records were obtained from the Pourtales Terrace, while the remaining ones came from the northwestern end of the Great Bahama Bank, the Northwest Providence Channel and along the western side of the Little Bahama Bank (Fig. 5).

Fig. 5. Distributional pattern of Homota barbata collected by the GERDA

The bathymetric range ofH. barbata on the insular side of the Straits is delineated along the 200 fm isobath (366 m) exceptionally extending beyond the 300 fm line (549 m). Conversely, on the continental side the species seems to favor shallower depths well within the shelf province.

Remarks. Previous reports of H. barbata in the Straits are known from the shoals off Key West and Dry Tortugas (Rathbun, 1937), and from two COMBAT stations made on the middle continental shelf off Key Largo (COMBAT stations 455 and 457).

Ecological note. The distribution of this homolid in the Straits is influenced by the interaction of temperature and depth. The normal depth range of this crab enables it to invade suitable habitats in either the shelf or the upper slope environment. This capacity seems further accentuated in the Straits due to the unique hydrographic conditions prevailing in the area. By examining the vertical dispersions of H. barbata it is evident that the species seldom exceeds depths beyond the 300 fm contour (549 m) where water temperature usually remains above 10° C. On the continental side, the drastic sloping of the isotherms forces the species to occupy much shallower habitats in waters warmer than 14°C. This fact may be held accountable for the pronounced insularity ofH. barbata at depths in excess of 200 m.

The limited substrate data available for this homolid indicated bottoms consisting of soft mud, shell/sand, and rocks.

Geographic range. Eastern Atlantic; Bahamas; Cuba; southwestern Gulf of México; Leeward Islands.

Bathymetric range. 604 to 1601 m.

Material examined. G-109, 1 m; G-963, 2 m; 6-94, 1 m; G-103, 1 f; G-446, 1 ovigerous f; G-293, 2 m; 1 ovigerous f; G-354, 1 m, 2 ovigerous f; G-357, 2 m, 1 ovigerous f; G-403, 1 m, 1 ovigerous f; G-448, 1 m; G148, 1 ovigerous f; G-372, 1 m, 1 f.

Distributional analysis. H. rostratus is included among the common deep-water brachyrans of the Straits (Fig. 1). A total of 21 specimens was identified of which 7 were gravid females; its sex ratio was roughly 1: 1. The coefficient of dispersion computed for the species (CD = 1.9) approaches significantly the unity value expected for a Poisson distribution.

The distributional pattern of H. rostratus is confined to the deepest region of the Straits, namely the central and southern sectors. There were some records taken from the lower northern Straits between the area of Orange Cay and Bimini, and other were recovered from the western side of Cay Sal Bank and the lower Keys, a single occurrence was obtained from the Blake Plateau (Fig. 6).

The horizontal dispersion of H. rostratus in the Straits seems closely associated with the depth favored by this homolid. The area where the axial floor of the Straits becomes shoaler, approximately at the vertix of the 450 fm contour (824 m), coincides with the northern most point of dispersion of the species, which reappears again where the bottoms drops down to more than 400 fm (732 m) near the Blake Plateau. It was in the proximity of this locality that the ALBATROSS dredged one of the few specimens known at the time. Towards the southern Straits, the bathymetric range of the species extends between the 500 and 600 fm contours (915 to 1098 m), and apparently becomes progressively deeper along the northern and southern coast of Cuba.

Remarks. H. rostratus was reported from the southwestern quadrant of the Gulf of México by Pequegnat (1970), who considered it extremely rare. Based on previous dredging records, Pequegnat estimated the center of the population to be about 500 fm (915 m), which nearly coincides with the mean depth of occurrence calculated for the species in the Straits (513 fm or 939 m).

Ecological note.Substrate data were available for eight of the twelve localities in which H. barbata occurred. On the basis of this information, two distinct biotopes were recognized: the first corresponded to the southern Straits where the predominant elements were mud and pteropod shells, while the second was situated at the base of the insular slope near the area where thethalweg plain of the Straits becomes shoaler; this last biotope was hard, made up of coral rubble, and probably corresponded to the rough surfaces described by Hurley et al. (1962) as typical of the insular slopes.

Fig. 6. Distributional pattern of Homologenus rostratus collected by the GERDA

Homola vigil (A. Milne Edwards, 1880)

Description.Telxiope vigil, Rathbun, 1937, p. 66, Figs. 1-3. Chace, 1940, p. 9.

Geographic range. From the coast of Georgia to the Windward Islands; north and south coast of Cuba.

Bathymetric range. 309 to 805 m.

Material examined. G-697, 1 m.

Distribution analysis. The single occurrence of this uncommon homolid crab was obtained from the upper slope of the southwestern end of the Little Bahama Bank. Eventhough H. vigil is known to be distributed as far north as off the coast of Georgia (ALBATROSS station 2415), no previous record of the species existed in the Straits.

Latreillia manningi Williams, 1982

Description. Williams, 1982, p. 233, figs. 1b-c, 2a-e, 3a, 8.

Geographic range. Nantucket shoals off Massachusetts to off Havana, Cuba; Venezuela; Ascencion Island.

Bathymetric range. 82 to 494 m.

Material examined. G-864, .1 ovigerous f; G-1102, 1 j, 1 ovigerous f; G-934, 1 ovigerious f; G-972, 1 m, I ovigerous f; G935, 1 f; G-836, 1 m, I ovigerous f; G-974, I ovigerous f; G-865, 1 ovigerous f; G-863, 1 m; G-579, I m; G-132 , 1 ovigerous f, I j; G233, 1 f, 3 j; G-234, I j; G-236, I j; G-242, 1 j; G-275, 1 ovigerous f; G-276, 1 j.

Distributional analysis. L. manningiis a common species in the Straits whose frequency rank (8th) is shared by two other important components of the brachyuran community, one a majid and the other a parthenopid (Table 1). As a general rule, in the 17 GERDA stations in which this species occurred, more than a single individual was seldom captured from each haul even though most records seem to have come from localities in close proximity one to another. Nevertheless, the computed coefficient of dispersion of L. manningi (CD = 2. 1) remains above the significance level expected for a random distribution. A total of 27 individuals was collected, the females predominant over the males by a 2:1 ratio. Worth noting here is the fact that 90 % of the females were ovigerous.

L. manningi appears evenly distributed on both sides of the Straits; 9 out of the 17 records were taken exclusively from the Pourtales Terrace while the remaining were scattered along the northwestern edge of the Great Bahama Bank from off Riding Rocks to Bimini and at the north end of the Little Bahama Bank (Fig.7).

Fig.7.Distributional pattern of Latreillia manningi collected by the GERDA

The bathymetric range ogL. manningi is markedly shallower on the continental side than on the insular margin; along the Pourtales Terrace the species displays a depth range of 174 to 302 m with an average depth at about 234 m. In contrast, on the insular side the species often occurs at depths within the 200 fm contour (366 m), reaching a maximum depth of 494 m off Bimini.

Remarks. Most of the previous records ofL. manningi in the Straits were obtained by the FISH HAWK (Stations 7298 and 7280), and by J. B. Henderson (fide Rathbun, 1937) from the edge of the continental shelf off the key West area. From the ATLANTIS expedition, Chace (1940) reported L. manningi from the Old Bahama Channel.

Ecological note. The distributional pattern of L. manningi in the Straits is one which perhaps best illustrates the dependence of a species upon nature of the substrate. This species shows a marked preference for rugged bottoms composed of rocks and coral rubble which are known to characterize the surface of the Pourtales Terrace and the western edge of Bahama Bank; of the nine substrate entries in our records, six indicated the existence of rock/ coral rubble bottom and the remaining three indicated shell rubble.

Cyclodorippe bouvieri Rathbun, 1934

Description . Rathbun, 1937, p. 106, pl. 32, figs. 3-4, pl. 81, figs. 1-2.

Geographic range.Straits of Florida; off Cuba and Puerto Rico.

Bathymetric range. 275 to 549 m.

Material examined. G-688, 3 m.

Distributional analysis. The single record of this rare brachyuran was from the southern end of the Little Bahama Bank at a depth of 492 m. Prior to this study, C. bouvieri was only known from off Habana (BLAKE station 53), Puerto Rico (JohnsonSmithsonian Expedition, stations 100 and 101, fide Rathbun, 1937), and from an OREGON station (No. 1005) located at the edge of the continental shelf southwest of Dry Tortugas (Chace, In: Springer and Bullis, 1956).

Cyclodorippe antennaria A. Milne Edwards, 1880.

Description. Rathbun, 1937, p. 104, text-fig. 24, pl. 32. figs. 1-2..

Geographic range.Straits of Florida; southeastern quadrant of the Gulf of México, and the West Indies.

Bathymetric range. 92 to 686 m.

Material examined. G-968, 1 f; G-984, 1 m; G-1009, 1 ovigerous f; G-706, 3 m. I f.

Distributional analysis. C. antennaria was captured occassionally by the GERDA at the western end of the Pourtales Terrace just off the Marquesas Keys, the eastern and northwestern side of Cay Sal Bank, and at the southern region of the Little Bahama Bank. Most of these records fall within the 200 frn isobath (366 m).

Remarks. This is the first time C. antennaria is reported from an area north of Cuba. The geographic range of this dorippidid crab may be considered representative of the Caribbean elements which are found scattered throughout the West Indian region, reaching their northern point of dispersion in the vicinity of the Straits and the Bahama Islands. The radiation of the species into the Gulf of México seems restricted to the southeastern region (Pequegnat, 1970).

Cyclodorippe agassizii A. Milne Edwards, 1880.

Description.Milne Edwards and Bouvier, 1902, p. 94, pl. 19, figs. 1-7, pl. 20, figs. 1-3- Rathbun, 1937, p. 105, text. fig. 25, pl. 32, figs. 5-6.

Geographic range. Blake Plateau; south coast of Cuba; Puerto Rico, and Lesser Antilles.

Bathymetric range. 232 to 558 m.

Material examined. G-405, 1 f; G-926, I ovigerous f.

Distributional analysis. C. agassiziiis also a very rare species whose occurrences in the Straits were limited to two female specimens, one ovigerous from the northern end of the Great Bahama Bank just east of the Great Bahama Bank just east of the Isaac Light, and from the Blake Plateau, respectively; both of these records were obtained at very similar depths (534 and 558 m). No previous report of this species is known from the above localities, thus extending northward its geographic range from the former northern limit of Bahía de Cochinos, Santa Clara Province, Cuba (Chace, 1940).

Cymopolus agassizii A. Milne Edwards and Bouvier, 1899

Description. Rathbun, 1937, p. 100, pl. 30, fig. 2, pl. 3 1, fig. 2.

Geographic range.Straits of Florida to Puerto Rico.

Bathymetric range. 128 to 549 m. Material examined. G-579, 1 ovigerous f.

Distributional analysis. The single record of this species was obtained from the outer shelf region off Key West.

Clythrocerus granulatus (Rathbun, 1898)

Description.Rathbun, 1937, p. 119, text-fig. 31, pl. 33, figs. 5-8. Williams et al. 1968, p. 45, text-fig. 3.

Geographic range. Off North Carolina; Straits of Florida to Venezuela.

Bathymetric range.146 to 1036 m.

Material examined. G-697, 1 m, 3 ovigerous f, 3 f.

Distributional analysis. Only seven specimens of this rare dorippidid were taken from a haul made by the GERDA near the southwestern corner of the Little Bahama Bank at a depth of 210 m. Earlier records of C. granulatus in the Straits were obtained by J. B. Henderson (fide Rathbun, 1937) from the outer shelf off the lower northern Straits, off Fowey Rocks, Ragged Key, Sand Key and Ajax Reef.

Clythrocerus nitudus (A. Milne Edwards, 1880)

Description.Rathbun, 1937, p. 109, text-figs. 26, 27, pl. 33, figs. 1-2.

Geographic range.South Carolina to West Florida and Grenada.

Bathymetric range. 12 to 531 m.

Material examined. G-886, 6 m, 8 ovigerous f; G665, 2 ovigerous f; G-864, 2 m; G-795, I soft; G-863, I m; G-1102, 6 m, 1 j; G-482, 1 m; G- 133, 1 m, 3 f ; G-606, 2 f ; G-580, 2 m; G- 145, 1 f; G-457, I f.

Distributional analysis. C. nitidusrepresents a conspicuous element among the brachyuran assemblages of the Pourtales Terrace. According to its frequency of occurrence and relative abundance throughout the GERDA collection, C. nitidus falls within the category of dominant species (Fig. 1). The coefficient of dispersion of the species (CD = 7.3) shows a significant departure from the unity value expected for a Poisson distribution, which indicates a clumping spatial dispersion of the individuals. A total of 38 specimens was identified having an almost equal ratio between females and males; 10 out of the females were ovigerous.

With the exception of a single occurrence of C.nitidus on the Blake Plateau, the distribution of this species is centered around the Pourtales Terrace (Fig. 8).

Its bathymetric range extends from the outer shelf region to the upper continental slope, though most of the individuals tend to occur at about 200 m.

Ecological note. Ever since the early explorations conducted in the Straits, C. nitidus has always been a common element in the collection made on the continental margin of the Florida Keys, particularly in the regions off Fowey Rocks, the Pourtales Terrace, and the vicinity of Key West. This small dorippidid crab exhibits such a defined preference for irregular and hard substrates that it may well be regarded as a good indicator of bottoms composed of rocks, crushed coral, and shell rubble/mud or sand. This partly would explain its considerable concentration in the area of the Pourtales Terrace. However, the absence ofC. nitidus from the western edge of the Bahama Bank, where bottom configuration is somewhat similar to that of the above Terrace, cannot be satisfactorily explained with the information on hand.

Cymonomus quadratus A. Milne Edwards, 1880

Description. Rathbun, 1937, p. 98, text-fig. 23, pl. 30, fig. 30, pl. 3 1, fig. 3.

Geographic range. Straits of Florida; Gulf of México to Lesser Antilles.

Bathymetric range. 185 to 930 m.

Material examined. G-1099, I m; G-365, 1 j.

Fig.8. Distributional pattern of Clythrocerus nitudus collected by the GERDA

Distributional analysis. The two records of C. quadratus were obtained from the Pourtales Escarpment between the area of Key West and Dry Tortugas , at depths ranging from 622 to 694 m. The only previous record of this species in the Straits came from a location northwest of Dry Tortugas (BLAKE station 45).

Ethusina abyssicola Smith, 1884

Description. Rathbun, 1937, p. 91, text-fig. 21, pl. 26, fig. 1, pl. 27, fig. 1.

Geographic range. Eastern Atlantic, in the vicinity of Spain , to west coast of Africa; Western Atlantic, from Southern New England to Brazil; Gulf of México, except southeastern quadrant.

Bathymetric range. 860 to 4026 m.

Material examined. G-963, 1 f; G- 1107, 1 m; G-965, 1 f.

Distributional analysis. E. abyssicola is perhaps the only truly abyssal element that forms part of the deep brachyuran community of the Straits. The records of this species were obtained from the southern and central Straits at depths in excess of 900 m.

Remarks. Pequegnat (1970) has suggested the possibility that there may be more than one species of the genusEthusina distributed in the Western Atlantic. He based his asumption on certain morphological differences observed in specimens form the Gulf of México, wichi somewhat resemble some of the characters ofE. faxoni, a species with a much deeper range thanE. abyssicola. Pequegnat himself, emphasized the remarkable depth hiatus of about 1,000 fm (1830 m) observed in the bathymetric range ofE. abyssicola. In the present study two of the records ofE. abyssicola were obtained within the 800 fm contour (1464 m), and a third on a shallower depth (892 m). However, this apparent gap is not significant enough to assume any population differences.

Ecological note. Substrate data available indicated mud and pteropod ooze as the predominant materials in the localities where the species was captured.

Ethusa microphthalma Smith, 1881

Description. Rathbun, 1937, p. 82, pl. 22, fig. 3, pl. 23, fig. 3.

Geographic range. Western Atlantic from Massachusetts to Cuba, northeastern Caribbean Sea, and in all section of the Gulf of México.

Bathymetric range. 110 to 752 m.

Material examined. G-826, I m; G-1099, 1 f; G1085, I f; G-110, 1 m; G-657, 1 f; G-507, 1 m; G76, 1 m; G-238, 1 j; G-432, 1 j; G-462, 2 m.

Distributional analysis. In spite of the reduced number of individuals of E. microphthalma captured, this species may be included among the common elements of the brachyuran fauna of the Straits in view of its consistent occurrence in the GERDA collection; of the eleven specimens identified, six were males, three females, non of them ovigerous, and the remaining were juvenile stages. The coefficient of dispersion calculated for the species (CD = 1.15) lies within the significance level expected for a random spatial dispersion.

E. microphthalma was found distributed at the upper and lower sectors of the northern Straits, off the St. Lucie Inlet, and off Biscayne Bay, respectively. It also occurred at the Western end of the southern Straits Between the Marquesas Keys and Dry Tortugas; at about 25° 20' N latitude, the species spreads across to the insular side, having been collected off Riding Rocks, and north of Bimini (Fig. 9).

The bathymetric range of E. microphthalma extends from the edge of the continental shelf down to the upper slope region. On the continental side, the species favors depths closer to the 100 I'm isobath (183 m) whereas on the insular side it mainly occurs along the 200 fm isobath (366 m).

Remarks. The only previous records known of E. microphthalma in the Straits were those given by W. L. Schmitt (fide, Rathbun, 1937) from the outer shelf and upper slope off Dry Tortugas. This seems to be the normal range of this species as attested to by the records given by Pequegnat (1970) and Soto (1972) from the Gulf of México.

Ecological note. The dispersion of E. micromphthalma in the area of study is essentially controlled by both depth and the substrate nature. The apparent discontinuity of this species at the central Straits, particularly along the Pourtales Terrace, is indeed a result of the substrate requirements of this dorippidid crab. In all the localities in which E. microphthalma was found, the bottoms were characterized by unconsolidated sediments composed by either mud and pteropod tests or by different gradations of sand and mud.

Ethusa tenuipesEthusa tenuipes Rathbun, 1897

Description Rathbun, 1937, p. 87, pl. 24 fig. 3, pl. 25, fig. 3

Geographic range. Off North Carolina; Straits of Florida to the Gulf of Mexico; north and south coast of Cuba.

Bathymetric range. 84 to 395 m.

Material examined. G-725, 1 m, 1 f; G-236, 1 j; G270, I f; G-274, 1 f; G-426, 1 f.

Distributional analysis. E. tenuipes is essentially a shelf faunal component that normally extends its depth range onto the upper slope habitat. In the Straits, at depths greater than 200 m, the species is mainly confined to the insular side from off Riding Rocks to the Great Isaac Ligth. The only single occurrence of E. tenuipes on the continental side, was secured by the GERDA off key Largo at 146 m.

Fig. 9. Distributional pattern of Ethusa microphthalma collected by the GERDA

Remarks.According to the records of E. tenuipes given by Rathbun (1937), this dorippidid has been reported from both the inner and outer shelf off Miami down to the area of Key West and Dry Tortugas. The limited number of GERDA records obtained in this particular see tor of the Straits can perhaps be ascribed to the inability of E. tenuipes to penetrate the 10°C isotherm. The shoaling of this thermal boundary along the Florida side critically reduces the chance of settlement of the species on the transitional area between the shelf and the slope environment.

The northern geographic range of this dorippidid was extended to the outer shelf off North Carolina from its former northern limit on the east coast of Florida (Williams et al., 1968). the outer shelf region also seems to be the normal habitat of E. tenuipes in the eastern half of the northern Gulf of México (Soto 1972).

Myropsis quinquespinosa Stimpson, 1871

Description. Milne Edwards and Bouvier, 1902, p. 110, pl. 21, figs. 4-6, pl. 22, figs. 1-5. Rathbun, 1937, p. 164, pl. 46, figs. 1-3.

Geographic range. Massachusetts to Venezuela.

Bathymetric range. 24 to 1047 m.

Material examined. G-857, 1 f; G-1083, 1 f; G-110, 1 j; G-507, 2 m, 1 f; G-174, 1 f; G-236, 1 m; G-238, 3 m, 3 f, 4 j; G-251, 1 m, 1 f; G-270, 1 m; G-276, 1 m; G274, 1 f; G-275, 1 f; G-276, 1 j; G-432, 1 f; G-400, 3 m, I f, 2 ovigerous f; G-459, 1 f; G-460, 3 m, 1 f, 2 ovigerous f; G-462, 6 m; G-510, 1 f; G-930, 1 m; G959, 1 j; G-984, 2 f; G-1009, 1 f; G-1206, 1 m, G1327, 2 m; G-720, 1 j.

Distributional analysis. M. quinquespinosarepresents the third most frequent component of the deep brachyurans inhabiting the Straits (Table 1); however, because of its low average number of individuals per sample (2.0), it was included among the common species (quadrant IV, Fig. 1). A total of 55 specimens were identified having a sex ratio of roughly 1: 1; just four ovigerous females were observed. The coefficient of dispersion of M. quinquespinosa (4.3) partially suggests an aggregative pattern of spatial dispersion.

M. quinquespinosa appeared thoroughly distributed in the area of study. In the northern Straits the species occurred on the outer continental shelf off the St. Lucie Inlet and off Key Largo. Two records were obtained from the northwestern and eastern side of Cay Sal Bank; most of the records from the southern Straits came from the outer shelf of the area between Dry Tortugas and the Marquesas Keys. Its insular distribution started at about Riding Rocks and continued all along the northwestern corner of the Great Bahama Bank, entered the mouth of the Northwest Providence Channel, and reappeared on the north side of the little Bahama Bank and the Blake Plateau. (Fig. 10).

The depth range of M. quinquespinosaon the continental side of the Straits follows a defined pattern delineated by the 100 fm contour (183 m.); on the insular side the species occupied a deeper stratum very close to the 200 fm contour (366 m.)

Remarks. Earlier records of M. quinquespinosa in the Straits are known from the collections made by W. L. Schmitt on the outer shelf off Dry Tortugas; subsequent records have been provided by the exploratory fishing vessels COMBAT and OREGON from the western edge of the Bahama Bank (COMBAT and OREGON from the western edge of the Bahama Bank (COMBAT stations 235, 445 and 446; OREGON stations 1336 and 1343).

Ecological note. The distribution of M. quinquespinosa in the Straits seems controlled by the optimum depth range of this leucosiid rather than by its thermal tolerance or substrate preferences. On the basis of the information given herein as well as on recent reports by Pequegnat (1970) and Soto (1972), this species may be designated as a characteristic faunal component in the assemblage of elements that inhabit the transitional region between the outer continental shelf and the upper portions of the slope. The close packing of the isotherms on the Florida side does not cause a major effect on the vertical dispersion of the species which tends to maintain depth levels where water temperature remains roughly above 14º C.

M. quinquespinosa exhibits certain plasticity in regard to the selection of a substratum; along the insular margin of the Straits the species exclusively occurs on rubbly bottoms composed of biogenic materials such as echinoderm tests, clam fragments, and coral remains, whereas on the Florida side it tends to occur on soft bottoms made up of mud ooze, sand, and pteropod tests.

Iliacantha subglobosa Stimpson, 1871

Description. Rathbun, 1937, p. 185, pl. 53, figs. 1-2 Williams, 1965, p. 150, fig. 128.

Geographic range. Western Atlantic, from North Carolina through the Antilles, to State of Alagoas, Brazil.

Bathymetric range. 28 to 394 m.

Material examined. G-725, 2 m; G-522, 3 m; G-692, 1 m; G-274, 1 m; C-251, 1 f; G-390, 1 f; G-695, 1 f.

Distributional analysis. I. subglobosa is essentially a shelf-faunal component which was occasionally captured by the GERDA. Only eleven individuals were collected, the males predominant over the females by a 2:1 ratio. The coefficient of dispersion of the species (CD = 1.7) shows no significant aggregation in its spatial distribution due, perhaps, to the limited records obtained.

The distributional pattern of this species in the Straits, at depth in excess of 200 m, is entirely confined to the insular sector; its apparent absence from the continental side, can be explained by its normally shallower range near the mainland. The insular records were taken from the northwestern corner of the Great Bahama Bank from about Sandy Cay to a few miles east of the Great Isaac Light; other records came from the southwestern and northwestern ends of the Little Bahama Bank. (Fig. 11).

Fig. 10, Distributional pattern of Myropsis quinquespinosa collected by the GERDA

The bathymetric range ofI. subglobosa extends from the proximity of the outer shelf, or about 176 m, down to 565 m, near the mouth of the Northwest Providence Channel; this last record extends its depth range approximately 271 m. The average depth computed for the species (320 m) lies close to the 200 fm contour.

Remarks. The reports given by Rathbun (1937) indicate the presence of I. subglobosa on the continental shelf from Miami to the Key West and Dry Tortugas area. An additional report is given by Chace (In: Bullis and Thompson, 1965) from a COMBAT station (237) located north of the Little Bahama Bank at a depth of 215 fm (394 m).

Paracyclois atlantis Chace, 1939

Description. Chace, 1940, p. 27, text-figs. 11-12.

Geographic range. North coast of Cuba to the Little Bahama Bank.

Fig. 11. Distributional pattern of -Riacantha sublobossa collected by the GERDA

Bathymetric range.169 to 430 m.

Material examined. G-393, 1 f; G-1329, 2 m, 1 f.

Distributional analysis. The two occurrences of this deep-water crab were taken from the Northwest Providence Channel east of the Great Isaac Light at a depth of 252 m and at the northwestern corner of the Little Bahama Bank at 169 m. These records extend its geographic range northward from that of early reports the northern coast of Cuba (Chace, 1940).

Calappa angusta A. Milne Edwards, 1880

Description. Rathbun, 1937, p. 210, pl. 64, figs. 1-6. Williams, 1965, p. 154, fig. 134.

Geographic range. Off Cape Lookout, N.C., through eastern Gulf of México, to Grenada.

Bathymetric range. 9 to 275 m.

Material examined. G-757, 1 m, I j; G-681, 1 j.

Distributional analysis. C. angusta is seldom found outside the continental shelf boundaries. The only two records obtained during theGERDA's operation in the Straits were from the outer shelf off Key Largo and from a locality in the Northwest Providence Channel just north of the Great Bahama Bank. This species is known to inhabit the continental margin of the Florida Keys from off Miami to Dry Tortugas (Rathbun, 1937; Chace In Springer and Bullis, 1956).

Acanthocarpus bispinosus A. Milne Edwards, 1880

Description. Milne Edwards and Bouvier, 1902, p. 127, pl. 24, fig. 12, pl. 25, figs. 4-6. Rathbun, 1937, p. 224, pl. 68, figs. 1-3.

Geographic range. Straits of Florida to Windward Islands.

Bathymetric range.247 to 361 m.

Material examined. G-467, 1 m.

Distributional analysis. The single occurrence of A. bispinosus was obtained from the upper continental slope off Dry Tortugas at a depth of 357 m; substrate data available for this locality indicated soft mud bottom. Worth noting is the fact that all previous reports of this uncommon calappid crab seem to have been taken from the same location near Dry Tortugas (Rathbun, 1937; OREGON stations: 1007, 1320), and no other findings are known aside from that of the type locality in the Grenadines, Lesser Antilles.

Acanthocarpus alexandri Stimpson, 1871

Description. Williams, 1965, p. 156, fig. 137.

Geographic range. Massachusetts to the Northeastern Gulf of México; Puerto Rico to Grenadines; Brazil.

Bathymetric range. 57 to 1034 m.

Material examined. G- 110, 4 m; G- 173, 8 m; G712, 1 m; G-676, 4 j; G-823, 1 m; G-857, 1 j; G-1083, 6 j; G-507, 1 m; G-1099, 2 j; G-21, 2 m, 2 j; G-172, 7 j; G-174, 5 m, 2 f, 3 j; G-432, 6 j; G-459, 4 m; G-460, 5 j; G-462, 3 m, 7 j; G-452, 2 j; G-657, 1 m; G-1085, 3 m, 1 f.

Distributional analysis. A. alexandriis a common element among the deep brachyurans of the Straits, which ranks 7th according to its frequency of occurrence and 5th by its relative abundance (Tables 1 and 2); in the 81 specimens identified, the males far outnumbered the females by a factor of ten, though nearly 50 % of the individuals were juvenile stages. The coefficient of dispersion of this species (CD = 6) suggested a clusttering type of spatial dispersion.

The distributional pattern of A. alexandri may be categorized as continental despite two isolated records obtained in the insular sector of the Straits (Fig. 12). On the continental side the species spreads from the upper and lower region of the northern Straits to the western end of the southern Straits; interestingly enough, no records of this calappid were recovered from the Pourtales Terrace itself, nor from the Cay Sal Bank area; records from the northern Straits included the following localities: of the St. Lucie inlet and the Lake Worth, off Miami, and Key Largo. Those obtained from the southern Straits were taken in the area between the Marquesas Keys and Dry Tortugas. The two insular records came from the northwestern corner of the Great Bahamas Bank.

The bathymetric distribution of A. alexandri seems confined to the outer shelf and upper slope habitats.

Remarks. According to earlier records of A. alexandri in the Straits (Rathbun, 19-37), the species is a normal inhabitant of the outer shelf region although it may also be found living in shallower depths. The exploratory fishing vessel COMBAT took this species from a locality north of Cay Sal Bank at a depth of 565 fm (1034 m.), which is actually the deepest known record for this calappid.

Ecological note. In addition to the defined bathymetric range of A. alexandri to the referred two habitats, its distributional pattern appeared closely associated to the regular bottoms of unconsolidated sediments found along the continental margin of both northern and southern sectors of the Straits. In the former sector, the combination of mud and shell rubble is fairly common whereas in the latter the predominant substrate materials are soft mud ooze, pteropod tests, and sand. The conspicuous absence of this calappid from the central Straits, particularly in the area of the Pourtales Terrace, may be caused to a certain extent by the rugged nature of the bottom in this part of the Straits; should this be the case, the scarcity of insular records for the species, can at least be partially ascribed to the highly irregular bottoms known to occur on the insular slope (Hurley et al., 1962; Staiger, 1970).

Cancer borealis Stimpson, 1959

Description.Rathbun, 1930, p. 182, text-fig. 30 Williams, 1965, p. 175, fig. 156.

Geographic range. Nova Scotia to south of Tortugas, Fla.; Bermuda.

Fig. 12. Distributional pattern of Acanthocarpus alexandri collected by the GERDA

Bathymetric range. Shallow water to 796 m.

Material examined. G-655, 4 m, 1 f; G-657, 1 j; G-857, 2 f, 1 j; G-61, 1 f; G-21, 1 f; G-172, 1 m, 1 f; G-173, 1 m; G-174, 1 m; G-413, 1 f; G659, 2 m; G-851, 1 f; G-855, 1 f; G-998, 1 m; G-999, 3 m, 5 f; G-997, 1 m, 1 f.

Distributional analysis. C. borealis is included among the ten most common species of brachyurans captured by the GERDA. Normally a good number of specimens was collected in the areas where this species was present, and on occasions as many as eight individuals were obtained from a single haul. According to its computed coefficient of dispersion (CD = 4), C. borealis follows a clumped type of spatial distribution. A total of 31 specimens was identified having almost an equal sex ratio; none of the females were gravid.

C. borealis appeared restricted to the continental side of the Straits, particularly to the northern sector (Fig. 13). Most of the records were obtained from both the outer shelf and upper slope off the St. Lucie Inlet while the remaining were recovered from the outer shelf off the Boca Raton Inlet, Miami, and the northern end of Key Largo.

The depth range of C. borealis in the Straits extended from 180 m to 541 m; however, 95 % of its populatin seems concentrated between 204 and 316 m.

Fig. 13. Distributional pattern Of Cancer borealis collected by the GERDA

Remarks.The only previous records of C. borealis in the Straits are those given by Rathbun (1930) from the upper slope near Cape Florida and those listed by Bullis and Thompson (1965) from an OREGON station (1543) located west of Dry Tortugas. This last locality represents the southern limit in the geographic distribution of this species.

Ecological note. The distribution of this temperate form into the Straits seems chiefly controlled by the interaction of temperature and substrate. In this particular case, the 10ºC isotherm constitutes the upper borderline in the vertical distribution of C. borealis. The actual interception of the referred isotherm on the Florida side takes place at depths that fluctuate from 150 to 400 m; such fluctuation nearly coincides with the normal upper depth range of the species in the area of study . In addition to this, C. borealis displays a marked preference for bottoms of fine texture primarily composed of mud and pteropod tests. This fact would partially explain its absence from the western edge of the Bahamas and the Pourtales Terrace where bottoms, as said earlier, are rather hard and irregular.

Cancer irroratus Say, 1817

Description Rathbun, 1930, p. 180, text-fig. 29, pl. 85, fig. 1. Williams, 1965, p. 175, fig. 155.,

Geographic range. Labrador to South Carolina, and the Straits of Florida.

Bathymetric range. Low water to 575 m.

Material examined. G-607, 1 m; 2 f; G-605, 1 f; G-851, 1 f; G-855, 1 m, 1 f; G-999, 4 m, I f; G-857, 1 f.

Distributional analysis. C. irroratus was captured only occasionally by the GERDA. This species is by far less numerous than its congeneric species C. borealis. From six GERDA stations just twelve specimens were taken. The females predominant over the males by a 2:1 ratio; no ovigerous females were present in the collection.

C. irroratus also appeared confined to the continental side of the Straits, occurring near the northern end of Key Largo and off Miami (Fig. 14); a single record was obtained from the thalweg plain between the upper northern Straits and the Little Bahama Bank.

The bathymetric range of this species extended from about 174 to 541 m, attaining its optimum depth at 255 m.

Fig. 14. Distributional pattern of Cancer irroratus collected by the GERDA

Remarks. The present report extends the southern geographic range of C. irroratus into the Straits of Florida proper; its previous southern limit was the area off Cape Cañaveral as reported from six COMBAT stations made on the upper continental slope (ChaceIn: Bullis and Thompson, 1965).

Ecological note. The ecological requirements ofC. irroratus are essentially the same as those outlined for its sympatric relative C. borealis. The depth range of these two especies in the Straits overlap to a considerable extended and they exhibit almost equal mean depth of occurrence.

Portunus (Achelous) ordwayi (Stimpson, 1860)

Description.Rathbun, 1930, p. 71, pl. 33. Williams 1965, p. 166, fig. 148.

Geographical range. Vineyard Sound, Mass.; North Carolina through Gulf of Mexico, Caribbean Sea and West Indies to State of Bahia, Brazil; Bermuda.

Bathymetric range. Surface to 284 m.

Material examined. G-32, 13 m, 16 f; G-1329, 1 f.

Distributional analysis. P. ordwayi is essentially an inshore portunid crab which rarely extends its range beyond the middle shelf region. The above two records were taken at very unusual depths for the species; one was taken from the upper slope off Miami at 235 m while the other was obtained at the northern end of the Great Bahama Bank at the depth of 284 m. Considering the swimming capacity attributed to most of the members of the family Portunidae and the type of gear employed in this study, it is possible that the above individuals were captured at much shallower depths, while the otter trawl was being retrieved.

The specimens from the insular side of the Straits were identified by Mr. John Park.

Portunus (Achelous) floridanus Rathbun, 1900

Description. Rathbun, 1930, p. 82, pl. 40.

Geographic range. Off North Carolina; Straits of Florida.

Bathymetric range. 64 to 210 m.

Material examined. G-984, 4 j; G-985, 3 j; G-986, 2 m.

Distributional analysis. The three records of this portunid are all from the northwestern corner of the Cay Sal Bank along the 100 fm contour (183 m); most of the individuals captured were juveniles.

Prior to this study, the reports of P. floridanus in the Straits were limited to the type material collected by the ALBATROSS off Key West at a depth of 45 fm (82 m) and to the one obtained by the COMBAT (station 457) off Key Largo at 65 fm (119 m). The geographic range of this portunid was extended northward by records obtained from two COMBAT stations (391 and 406) made on the continental shelf off the coast of North Carolina (ChaceIn: Bullis and Thompson, 1965).

Portunus (Achelous) spinicarpus (Stimpson, 1871)

Description. Rathbun, 1930, p. 92, pl. 45. Williams, 1965, p. 167, fig. 150.

Geographic range. From North Carolina to Sao Paulo, Brazil.

Bathymetric range. 9 to 549 m.

Material examined. G-482, 1 m; G-712, 1 m; G-683, 3 j; G-637, 4 m, 1 f; G-984, 3 j; G-985, 5 j; G-467, 1 m, 1 f; G-233, 1 m; G-236, 6 j; G-238, 1 m, 3 f; G-272, 2 m; G-274, 13 j; G-275, 2 m; G-276, 5 m, 1 ovigerous f; G-394, 1 m; G-685, 2 f.

Distributional analysis. P. spinicarpus is a common inhabitant of both the continental shelf and upper slope region of the Straits. Because of its high percentage of occurrence and the considerable number of specimens captured, this portunid falls into the category of dominant species. (Fig. 1).

The coefficient of dispersion of the species (CD=6) indicates a clustering pattern of spatial distribution. More than 50 % of the total 57 specimens identified were juveniles; the estimated sex ratio was 2:1 in favor of the males.

At depths in excess of 200 m the distributional pattern of P. spinicarpus appeared concentrated on the insular margin of the Straits (Fig. 15); records from this area were obtained from the northwestern corner of the Bahama Bank, from about Riding Rocks to the Great Isaac Light as well as from the southern and northwestern side of the Little Bahama Bank. In the central Straits,P. spinicarpus occurred at the northern end of Cay Sal Bank and across the Pourtales Terrace. In the southern Straits there was a single record from near Dry Tortugas.

Fig. 15. Distributional pattern of Portunus spinicarpus collected by the GERDA

The bathymetric range ofP. spinicarpus along the insular margin is defined near the 200 fm contour (366 m), whereas on the continental side the species is likely to remain within the inner shelf habitat.

Ecological note. The substrate data available for this portunid indicated the predominance of hard rugged bottoms composed of biogenic materials.

Benthochascon schmitti Rathbun, 1931

Description. Rathbun, 1931, p. 125, pl. 1. Pequegnat, 1970, p. 187, fig. 6.6.

Geographic range. South of Nantucket, Mass.; Straits of Florida; Gulf of México.

Bathymetric range. 201 to 511 m.

Material examined. G-659, 1 m; G-614, 1 m; G-655, 1 m; G-469, 3 m, 3 f, 3 j; G-21, 1 m; G-173, 1 m, 3 f; G-174, 1 m, 1 f; G-465, 1 m; G-1097, 1 f; G-1096, 4 m, 1 f; G-997, 3 m; G-1095, 1 f; G-845, 1 m.

Distributional analysis. B. schmitti is a fairly common component of the brachyuran community inhabiting the upper continental slope -of the Straits of Florida. According to its frequency of occurrence, this species has been ranked 11th together with five other important brachyurans of the families Cancridae, Xanthidae, Goneplacidae, and Majidae (Table 1). From 13 GERDA stations a total of 31 specimens were taken, the males predominant over the females by a 2:1 ratio; no ovigerous females appeared in the collection. The coefficient of dispersion of this portunid (CD = 5) departs from the value expected for a random type of dispersion, thus suggesting an aggregative spatial distribution of its individuals.

The distribution of B. schmitti in the Straits is restricted to the continental side from the western end of the southern sector to the lower and upper parts of the northern Straits (Fig. 16). The records from the first area were all from the upper slope of Dry Tortugas, whereas those from the second region are from the Miami Terrace and off the St. Lucie Inlet. Worth noting is the apparent absence of B. schmitti from the surface of the Pourtales Terrace.

Fig. 16. Distributional pattern of Benthochascon schmitti collected by the GERDA

The vertical distribution of this portunid exhibited a rather defined range delineated between the 100 and 200 fm isobaths (183-366 m), reaching its optimum depth at about 295 m.

Remarks. Up until now, B. schmitti was though to be one of the few brachyuran species indigenous to the Gulf of México (Pequegnat, 1970, Soto, 1972), and its nearest record to the area of the Straits was that of its first finding in the vicinity of Dry Tortugas by W. L. Schmitt in 1930. The records given herein confirm the existence of this deep-water portunid as a normal resident of the area of the Straits. Wigley and Messermith (1976) gave an account of a male specimen of B. schmitti caught south of Nantucket, Mass.; from a depth of 252 m ; however this occurrence is probably accidental in nature.

Ecological note.Undoubtedly the narrow depth range and the niche requirements exhibited by this portunid determine to a considerable extent its pattern of distribution in the Straits; its absence from the insular side, the Cay Sal Bank, and probably from Cuba as well may be justified by the inability of the species to bridge dephts greater than 279 fm (511 m). The biotopes thatB. schmitti occupies are characterized by poorly consolidated bottoms primarily composed of mud and shell fragments.

Bathynectes longispina Stimpson, 1871

Description. Bathynectes superba (Costa): Rathbun, 1930, p. 28, pls. 9-10.

Geographic range.From Marthas Vineyard, Mass., to the Gulf Stream in the Florida Straits; north and south coast of Cuba; Arrowsmith Bank, Yucatan, México.

Bathymetric range. 128 to 900 m.

Material examined. G-657, 5 m; G-757, 1 f; G-173, 1 m; G-605, 1 f; G-758, 2 m, 4 f; G-1084, 1 f; G-968, 1 m; G-29, 2 m, 5 f; G-145, 2 m, 2 f; G-227, 2 m, 1 f, ovigerousf; G-225, 2 m, G-413, 4 J; G-435, 3 j; G437, 3 m, G-451, 2 f, 1 ovigerous f; G-452, 2 m, 1 f, 2 ovigerous f, 1 j; G-464, 1 m, 1 j; G-480, 2 j; G-482, 2 j; G-484, 3 j; G-61, 1 m; G-21, 2 m, 2 f; G-45, 1 f; G824, 2 m, 6 f; G-1095, 1 f; G-969, 6 m, 4 f; G-1099, 3 f, 2 j; G-939, 1 m; G-835, 2 f; G-865, 1 m, 1 f; G-837, 1 f

Distribution analysis. B. longispina represents the second most frequent species and the third most abundant element in the GERDA collection (Tables 1 and 2). A total of 100 individuals were collected from 31 GERDA stations; the females slightly predominant over the males; only six ovigerous females were recorded. The coefficient of dispersion of the species (CD = 5) deviates significantly from the unity value of a Poisson distribution, thus suggesting a strong pattern of aggregation among its individuals.

The distributional pattern of B. longispina in the Straits appears restricted to the upper slope of the continental margin. The occurrences of the species extend from the western end of the southern Straits all along the Pourtales and the Miami Terraces to the upper northern Straits off the St. Lucie Inlet (Fig. 17).

The bathymetric range of this species is rather narrow, extending from the proximity of the outer shelf (174 m) down to about 403 m in the upper slope; the best estimate of the population center of this portunid may be situated at 259 m.

Remarks. The previous records of B. longispina in the area of the Straits were confined to localities off Key West (fide Rathbun, 1930). Later on, its geographic range was extended southward by the findings of the ATLANTIS in the north and south coast of Cuba (Chace, 1940); subsequent records of this portunid have been from the collections made by the OREGON and COMBAT in the proximity of Dry Tortugas (Chace In: Bullis and Thompson, 1965). Although it is very likely that this species enters at least some parts of the Gulf of México, its presence has gone undetected. During the preliminary study of the GERDA collection, I came across some specimens of B. longispina captured earlier by this vessel at Arrowsmith Bank off the Yucatan Peninsula.

According to Dr. Holthuis (personal communication), there is sufficient evidence at this point that warrants the separation of B. longispina andB. superba into two distinct allopatric elements; the former species is strictly confined to the Western Atlantic while the latter is restricted to the Eastern Atlantic.

Ecological note. This distribution of B. longispina in the Straits seems governed mainly by the depth restriction of the species rather by than its thermal tolerance or substrate preferences.

Fig. 17. Distributional pattern of Bathynectes longispina collected by the GERDA

The limited bathymetric range exhibited by this portunid may indeed prevent its spreading from the continental side to the western edge of the Bahamas Bank; such a restriction ought to be more critical in the deeper sectors of the Straits, namely the southern and central, whereas in the much shoaler northern sector B. longispina very likely occurs on both sides. In the course of this study, there were two instances in which this species was captured by plankton nets near the southwestern corner of the Little Bahama Bank.

The substrate data available for this species included a wide variety of bottoms which ranged from the fine mud and pteropod ooze materials that characterize the southern Straits to the rocky and rubbly floors of the Pourtales Terrace; the majority of individuals were recovered from this last type of substratum.

Portunus binoculus Holthuis, 1969

Description. Holthuis, 1969, p. .

Geographic range. Straits of Florida; Arrowsmith Bank, Yucatan, Mexico; Caribbean coast of Colombia and Panama.

Bathymetric range. 63 to 457 m.

Material examined. G-645, 1 ovigerous f; G-820, 1 m; G-1329, 1 m, 1 f.

Distributional analysis. The occurrence of P. binoculus in the Straits was limited to two records from the upper slope of the northwestern corner of the Great Bahama Bank and a third one obtained in the proximity of the Santaren Channel.

Allactaea lithostrata Williams, 1974

Description. Williams, 1974, p. 19, text-figs. 1-3.

Geographic range. Southeast of Cape Lookout, N. C., to the Straits of Florida; Cape Catoche, Yucatan, Mexico; off the coast of Venezuela.

Bathymetric range. 92 to 201 m.

Material examined. G-984, 1 m; G-408, 1 m, 1 f.

Distributional analysis. The records of this xanthid crab came from the northwestern end of Cay Sal Bank and from the inner shelf off Lake Worth at depths of 192 and 77 m respectively.

A. lithostrota was described by Williams from a specimen captured on the continental shelf southeast of Cape Lookout, N. C., a locality which apparently represents the northern limit in the distribution of this attractive looking crab. In addition to the above two records from the Straits, the species is also known to occur (Soto, 1980) off Cape Catoche, Yucatan R/V PILLSBURY, station 592, 21° 07' N, 86° 29' W), and as far south as the coast of Venezuela (R/V PILLSBURY, station 736, 10° 570 N, 65° 52' W).

Tetraxanthus bidentatus (A. Milne Edwards, 1880)

Description. Tetraxanthus rugosus, Rathbun, 1930, p. 459, pl. 185.Tetraxanthus bidentatus, Chace, 1939, p. 52.

Geographic range. Straits of Florida; northern coast of Cuba; Strait of Yucatan.

Bathymetric range. 165 to 536 m.

Material examined. G-938, 1 m; G- 1314, 1 m.

Distributional analysis. Only two records of this uncommon xanthid crab were taken by the GERDA in the area of the Straits. One of the specimens was taken near the mouth of the Northwest Prividence Channel at 536 m while the other came from the western end of the Little Bahama Bank at 498 m of depth.

T. bidentatus was first reported by Rathbun (1930) from the upper slope off Sand and Sambo Keys in the Straits as a new species, T. rugosus; later, Chace (1939) synonymized it under the nameT. bidentatus, which was first employed by A. Milne Edwards (1880).

Two additional specimens of T. bidentatus were found in the collection made by the GERDA on the western side of the Strait of Yucatan; this adds support to the possibility that the species may also be found inhabiting the Gulf of México, though no reports are yet known from that area.

Tetraxanthus rathbunae Chace, 1939

Description. Tetraxanthus bidentatus, Rathbun, 1930, p. 458, pl. 184. Tetraxanthus rathbunae, Chace, 1940, p. 52.

Geographic range. Western Atlantic from North Carolina to Grenada, along both coasts of Cuba, and southwestern and eastern half of the Gulf of Mexico.

Bathymetric range. 28 to 622 m.

Material examined. G-937, 1 f; G-1099, 1 f; G-237, 2 m; G-239, 1 f; G-1009, 1 f; G-657, 1 m, 2 f; G-110, 1 m, 1 ovigerous f; G-626, 2 f; G-465, 37 m, 5 f; G- 172, 1 f ; G- 174, 1 m; G -238, 4m; G-460, 8 m, 1 f, 1 ovigerous f; G-462, 9 m, 1 f, 1 ovigerous f.

Distributional analysis. T. rathbunae is another of the dominant species that integrate the brachyuran community inhabiting the transitional area between the shelf and the archibenthic provinces. A total of 83 specimens was obtained from 13 GE RDA stations, making this species the fourth most abundant element in the GERDA collection (Table 2). The calculated sex ratio was 3:1 in favour of the males; only nine ovigerous females were recorded. The large coefficient of dispersion obtained for the species (CD = 25) indicated the existence of a strong aggregative spatial distribution among its individuals.

T. rathbunae is distributed on both sides of the Straits. It occurred at the western end of the southern Straits, near Dry Tortugas, at the upper northern sector, off the St. Lucie Inlet, at the eastern side of Cay Sal Bank, and finally along the northwestern corner of the Great Bahama Bank (Fig. 18). The species was conspicuosly absent from the surface of the Pourtales Terrace.

Fig. 18. Distributional pattern of Tetraxanthus rathbunae collected by the GERDA

As in thee case of many other brachyurans included in the present study, the bathymetric range of T. rathbunae is sensibly deeper on the insular margin than along the mainland; in the first region, this xanthid crab tends to occur near the 200 fm contour (366 m) while in the second its depth range fluctuates about the 100 fm contour (183 m)

Remarks. The records of this species in the Straits are limited. Few specimens were reported by Rathbun (1930) from the outer shelf off Fowcy Rocks and in the proximity of Key West; later, the exploratory fishing vessel COMBAT provided an additional record (station 446) on the western Bahama Bank off Orange Cay (Chace In: Springer and Bullis, 1956).

Ecological note. The type of substrate and the temperature regime prevailing in the Straits are the two factors that seem to exert a major influence upon the horizontal and vertical dispersion of the species in question. This xanthid crab appears to have the ability to discriminate bottoms composed of poorly consolidated materials from those of coarse texture. Its occurrences in the Straits are exclusively in areas where the substrate is composed of fine mud, pteropod ooze, sand/mud and fragments of echinoid tests; this substrate preference is perhaps accountable for the obvious gap noted in the distribution of T. rathbunae along the Pourtales Terrace and lower portion of the northern Straits (Fig. 18).

The inability of this species to transgress the depth at which the 10° C isotherm intercepts both margins of the Straits determines the lower limit of its vertical dispersion. The drastic compression of the isotherms on the continental side probably forces the species to occupy biotopes adjacent to the outer shelf while on the insular this crab is able to descend deeper due to the isotherm tilting (Devany, 1969).

Pseudomedaeus agassizi (A. Milne Edwards, 1880)

Description. Leptodious agassizi, A. Milne Edwards, 1880, p. 270, pl. 49, fig. 3. Rathbun, 1930, pl. 141, figs. 4-5 Williams, 1965, p. 192, fig. 174. Pseudomedaeus agassizi, Guinot, p. 776, fig. 25.

Geographic range. From Cape Hatteras, N. C., to Louisiana; Virgin Islands.

Bathymetric range. 7 to 220 m.

Material examined. G-135, 1 f.

Distributional analysis. The single record of this xanthid crab was obtained from the Pourtales Terrace at a depth of 200 m. This seems to be an unusual depth for this species, which essentially inhabits the reef environment of the Straits.

In the review of some of the genera of the family Xanthidae made by Guinot (1976c), the new genusPseudomedaeus was established in which two allopatric species were included: one restricted to the Eastern Atlantic, P. africanus (Monod, 1956) and the other to the Western Atlantic,P. agassizii (A. Milne Edwards, 1880). Felder (1973) reported the latter species from the coastal waters off Lousiana, thus extending its geographic range into the northwestern Gulf of México.

Eucratodes agassizii A. Milne Edwards, 1880

Description. Rathbun, 1930, p. 471, pl. 190.

Geographic range. Straits of Florida; northern Gulf of México; Yucatán; Puerto Rico.

Bathymetric range. 156 to 395 m.

Material examined. G-626, 5 m; G-237, 1 m.

Distributional analysis. The two records of this uncommon species are both from the insular side of the Straits near the northwestern corner of the Great Bahama Bank and in the proximity of the Berry Islands at depths of 381 and 395 m respectively; only six male specimens were taken. No previous records of this xanthid crab existed in the area of study.

Pilumnoides nudifrons (Stimpson, 1881)

Description.Rathbun, 1930, p. 538, figs. 1-2.

Geographic range. Straits of Florida Barbados.

Bathymetric range. 137 to 556 m.

Material examined. G-842, 1 f.

Distributional analysis. The single record of this species is from the edge of the continental shelf southwest of Key Largo. The existing records of P. nudifrons in the Straits have mostly been in the proximity of Key West at depths ranging from 75 fm (137 m) to 304 fm (556 m).

Micropanope scultipes Stimpson, 1881

Description.Rathbun, 1930, p. 428, pl. 178, figs. 1-3. Williams, 1965, p. 193, fig. 175.

Geographic range. South Carolina to Port Aransas, Texas; West Indies to Barbados.

Bathymetric range.28 to 311 m.

Material examined. G-135, 1 m; G-837, 1 m, 1 f; G984, 2 f, 1 j.

Distributional analysis. Two of the records ofM. scultipes were from the surface of the Pourtales Terrace and a third one from the northwestern end of Cay Sal Bank at depths ranging from 193 to 220 m; the substrate material in these three localities was made up of rocks and coral debris. Earlier records of the species in the Straits are known from the vicinity of Dry Tortugas (Rathbun, 1930) and off Key Largo (COMBAT station 455).

Nanoplax xanthiformis (A. Milne Edwards, 1880)

Description. Micropanope xanthiformis, Rathbun, 1930, p. 442, pl. 180, figs. 7-8. Williams, 1965, p. 193, figs. 176, 1831.Nanoplax xanthiforms, Guinot, 1967, 362, fig. 16.

Geographic range. Cape Hatteras, N. C.; Florida through Gulf of México, and West Indies to Cabo Frio, Rio de Janeiro, Brazil.

Bathymetric range. 15 to 333 m.

Material examined. G-270, 1 m; G-986, 1 m.

Distributional analysis. The occurrence of M. xanthiformis in the GERDA collection was limited to just two localities, one off Bimini at 175 fm (320 m) and another at the northern end of Cay Sal Bank at 103 fm (189 m) Previous records of the species in the Straits have been from the area off Cape Florida and in the vicinity of Dry Tortugas.

Micropanope truncatifrons Rathbun, 1898

Description. Rathbun, 1930, p. 433, text-fig. 68, pl. 178, figs. 78.

Geographic range. Straits of Florida; off Havana and Yucatan.

Bathymetric range. 238 to 355 m.

Material examined. G-270, 1 f; G-986, 1 f.

Distributional analysis. The two single occurrences of this deep-water xanthid were from the northern end of Cay Sal Bank at 103 m and from the upper slope off Bimini at 318 m. These two findings extend the range of the species into the Straits from its previous northern limit off Havana, Cuba. Three additional female specimens ofM. truncatifrons were found in the collections made earlier by the GERDA in the vicinity of Arrowsmith Bank and the Strait of Yucatan. At present, this locality represents the southern geographic limit for the species. Guinot (1967) questionably referred M. truncatifrons to her new genusNanocassiope.

Neopilumnoplax americana (Rathbun, 1898)

Description. Pilumnoplax americana, Rathbun, 1918, p. 21, textfigs. 5. Williams et al., 1968, p. 52, texzt-fig. 9. Neopilumnoplax americana,Guinot, 1969, p. 689.

Geographic range. North Carolina to Florida Keys; Strait of Yucatan; Brazil; Arabian Sea; Indo-Pacific region.

Bathymetric range. 128 to 805 - m .

Material examiend. G-480, 1 f.

Distributional analysis. The single record of N. americana was from the central Straits on the surface of the Pourtales Terrace at a depth of 105 fm (192 m); substrate data for this locality indicated a sand and shell rubble bottom.

Guinot (1969), in her review of the Goneplacidae, synonymized the genus PilumnoplaxStimpson, 1858, under the generic name Neopilumnoplaxproposed by R. Seréne; this new genus includes the type speciesN. heterochir and N. americana.

Most of the earlier records of N. americana in the Straits have been obtained from the outer shelf and upper slope regions of the Pourtales Terrace and the lower Florida Keys, especially near the area of Key West (Rathbun, 1918). From a GERDA station made in the Strait of Yucatan at 136 fm (249 m), a single male specimen of N. americana was identified.

Chasmocarcinus cylindricus Rathbun, 1900

Description. Rathbun, 1918, p. 59, text-figs. 28-29.

Geographic range. Straits of Florida; Gulf of México; north and south coast of Cuba; Jamaica, and Puerto Rico.

Bathymetric range. 13 to 1967 m.

Material examined. G-275, 2 f; G-236, 1 m, 2 f; G238, 1 m.

Distributional analysis. This small goneplacid crab was captured only on the insular margin of the Straits at three nearby localities off Riding Rocks; the three records were all taken near the 200 fm contour (366 m); the substrate data available for two of these localities indicated the existence of a bottom composed of sand, algal growth and shell rubble.

No records of this species in the Straits exist prior to the present study.

Frevillea rosae A. Milne Edwards, 1880

Description. Frevillea rosae, Milne Edwards and Bouvier, 1923, p. 337, pl. 6, fig. 1. Goneplax rosae, Rathbun, 1919, p. 27. Chace, 1940, p. 47.

Geographic range. Straits of Florida to the north coast of Cuba; off St. Vincent.

Bathymetric range. 159 to 476 m.

Material examined. G-523, 1 m; G-238, 1 f; G-626. 1 f; G-1327, 1 f.

Distributional analysis. The four records of this uncommon goneplacid were obtained from the norhtwestern corner of the Great Bahama Bank, and at the entrance of the Northwest Providence Channel; these records were all from near the 200 fm contour (366 m) which coincides with the insular depth range given by Chace (1940). These findings are the first of this species in the area of the Straits of Florida.

Frevillea hirsuta (Borradaile, 1916)

Description. Goneplax hirsuta,Rathbun, 1918, p. 28, text-fig. 7. Williams, 1965, p. 201, fig. 184. Frevillea hirsuta Guinot, 1969, p. 513, pl. 2, fig. 3, text-figs. 40, 58-59.

Geographic range. North Carolina to Rio de Janeiro, Brazil; Northeastern Gulf of México.

Bathymetric range. 73 to 476 m.

Material examined. G-272, 1 m; G-683, 2 m, 2 f, 1 ovigerous f; G-390, 2 m; G-681, 1 m; G-1329, 1 f; G927, 1 f.

Distributional analysis. F. hirsuta appeared sporadically in the GERDA collection. Only 11 individuals were obtainded from six GERDA stations, in which the males and females occurred in almost equal proportion; a single ovigerous female was recorded.

The distributional pattern of this goneplacid in the Straits at depths in excess of 200 m is entirely concentrated on the insular slope of the western edge of the Bahama Banks including the entrance to the Northwest Providence Channel .

The vertical dispersion of the especies is limited to the upper levels of the slope occurring from 210 to 476 m and with a mean depth of occurrence of about 299 m.

Frevillea barbata A. Milne Edwards, 1880

Description. Goneplax barbata.De Rathbun, 1918, p. 26, pl. 4, figs. 1, 3, pl. 5. Frevillea barbata Guinot, 1069, p. 513, pl. 11, fig. 2.

Geographic range. Straits of Florida; Gulf of México to Grenada, West Indies; Yucatan Channel.

Bathymetric range. 55 to 201 m.

Material examined. G-982, I m.

Distributional analysis. This single occurrence ofF. barbata was obtained from the northern end of Cay Sal Bank at a depth of 201 m. The only previous report of this uncommon geneplacid crab in the Straits is that listed by Rathbun (1918) from a locality off Havana, Cuba.

Trizocarcinus tacitus Chace, 1940

Description. Chace, 1940, p. 41, text-fig. 15-16. Guinot, 1969, p. 518, figs. 34, 43, 45, 50, 51.

Geographic range. Straits of Florida; northeastern Gulf of México, and off Barbados.

Bathymetric range. 187 to 462 m.

Material examined. G-855, 1 f; G-969, 1 m; G-462, 1 m; G-696, 2 m.

Distributional analysis. T. tacitus occurred rather occasionally throughout the GERDA collection in the Straits. The four records of the species were from the upper slope (187 to 462 m) off the following locaties; south of the Marquesas Keys, northern end of Key Largo, and southern corner of the Little Bahama Bank. These are the first reports of the especies in the area of study.

Chace (1940) described this goneplacid crab from a specimen obtained by the BLAKE Expedition from a locality near Barbados (BLAKE station 274); it apparently was first overlooked by Milne Edwards, and then misidentified by Boone (1930) as Goneplax tridentata. Later on Chace himself provided the second record of this rare species form an OREGON station (173) made in the Northeastern Gulf of México (Springer and Bullis, 1956). From the brachyuran collection obtained by the R/V Pillsbury in the Caribbean, Holthuis (unpublished) identified an adult female specimen of T. tacitus captured off St. Vicent, in the Lesser Antilles (PILLSBURY station 876, 13°13.9' N, 61º 4.7'W).

Pseudorhombilia octodentata Rathbun, 1906

Description. Rathbun, 1918, p. 43, text-figs. 17-18, pl. 14, fig. 3. Guinot, 1969, p. 704, text-figs. 113-115, pl. 111, fig. 2.

Geographic range. Straits of Florida; north coast of Cuba; Dominica, Martinique.

Bathymetric range. 183 to 334 m.

Material examined. G-275, 1 m.

Distributional analysis. The only record of this rare goneplacid is from the western edge of the Great Bahama Bank off Riding Rocks at about 334 m; a similar depth for the species was reported by Chace (1940) for a male specimen taken by the ATLANTIS near the Old Bahama Channel off Punta Alegre, Cuba. This last locality was the former northern limit for this antillean species.

Robertsella mystica Guinot, 1969

Description. Pilumnoplax elata,Rathbun, 1918, p. 23, 24, pl. 3, fig. 1-2 (part: description of male).Robertsella mystica, Guinot, 1969b, p. 716, text-figs. 132-133, pl. 4, fig. 1.

Geographic range. Straits of Florida; Gulf of México, off Dry Tortugas.

Geographic range. Straits of Florida; Gulf of México, off Dry Tortugas.

Bathymetric range. 210 to 519 m.

Material examined. G-173, 1 m; G-658, 1 m; G-652, 1 m, 2 f; G-655, 2 m, 1 f; G-464, 2 m; G-855, 1 f; G1012, 1 f;G-1095, 1 m; G-997, 1 m; G-998, 2m; G659, 1f; G-654, 1m; G-15, 1 m. 1 f; G-77, 1 m; OREGON station 1330, 1 m Holotype).

Distributional analysis. R. mystica is a common deep-water crab frequently captured by the GERDA in the Straits. From 14 GERDA stations a total of 21 individuals were obtained, the males being predomiant over the females by a 2:1 ratio; no ovigerous females were taken. The compute coefficient of dispersion for the species (CD = 1.8) indicated a moderate departure from the significance level expected for a random distribution.

The distribution of R. mystica is essentially confined to the continental margin of the southern and northern sectors of the Straits (Fig. 19). Records of the species were from the upper slope south of Dry Tortugas, the Miami Terrace, and from the upper northern Straits just off the St. Lucie Inlet; only a single record of R. mystica was obtained at the southeastern corner of Cay Sal Bank.

The bathymetric range of this species extended from the edge of the continental shelf (210 m) down to about 519 m; however, 90 % of its population is centered around the 200 fm contour (366 m).

Remarks. The previous records of this goneplacid crab in the area of the Straits were limited the reports obtained by the ALBATROSS (station 2644), and the OREGON (station 1330) from off Cape Florida and Dry Tortugas, respectively.

Ecological note. The horizontal depersion of R. mystica in the area of study seems strongly influenced by its substrate preference while its vertical distribution is basically controlled by the interaction of temperature and depth. The substrate data available for the localities in which the species occurred clearly indicated the predominance of bottoms composed of fine-grained sediments, poorly consolidated materials, such as mud-pteropod ooze, and mud-sand occasionally combined with shell fragments.

On the other hand, the bathymetric range of R. mystica in the Straits maintains a significant correlation with the depth level at which the 10°C isotherm intercepts the various regions of the continental side; the depths of interception fluctuate from 150 to 400 m, but, in general, the 10°C borderline tends to be deeper in the southern and central Straits, sensibly shoaling towards the northern Straits; a similar effect is registered in the vertical dispersion of R. mystica whose upper range is roughly delineated by the depth level of the isotherm alluded to.

Thalassoplax angusta Guinot, 1969

Description. Pilumnoplax elata, Rathbun, 1918, p. 24, pl. 3, fig. 3 (part: description of male and growth variations ). Thalassoplax angusta Guinot, 1969b, text-figs. 131-132, pl. 4, figs. 2 Pequegnat, 1970, p. 192.

Geographic range. East coast of Florida and throughout the Gulf of México.

Bathymetric range. 183 to 752 m.

Material examined. G-172, 1 m; G-173, 5m; G-459, 1 m; G-460, 1 m; G-272, 1 f; G-657, 18 m, 1 ovigerous f; G-110, 3 m.

Distributional analysis. T. angusta falls within the category of brachyuran species which displayed low frequency values of occurrence and high average of individuals per sample (quadrant 11, Fig. 1); from a single haul made in the northern Straits as many as 19 individuals were captured and five other were obtained from a nearby locality; a total of 31 individuals were identified, the males being strongly predominant over the females. A single ovigerous female was recorded. The coefficient of dispersion of the species (CD = 13) strongly deviated from the level of significance for a random distribution, thus indicating a highly clumped spatial distribution.

T. angusta was found distributed on the outer shelf off Dry Tortugas and the upper northern Straits off the St. Lucie Inlet. The only insular record of the species in the Straits was taken near Sandy Cay.

Fig. 19. Distributional pattern of Robertsella mystica collected by the GERDA

The depth range of T. angusta along the continental side of the Straits is clearly delineated about the 100 fm contour (183 m) while on the insular side the species descends as deep as 370 m.

Pilumnoplax nitida Chace 1940

Description. Chace, 1940, p. 44, text-figs. 17, 18. Guinot, 1969, p. 689, text-figs. 116-118, 140.

Geographic range. Straits of Florida to the north coast of Cuba.

Bathymetric range. 348 to 476 m.

Material examined. G-237, 5 m; G- 1327, 3 m.

Distributional analysis. The only two records of this goneplacid crab were recovered from the northwestern corner of the great Bahama Bank; one was taken in the proximity of Riding Rocks and the other east of the Grat Isaac Light at depths of 395 and 432 m. The bottom trawls made in these localities yielded eight male specimens. These are the first findings of P. nitida in the area of the Straits proper. Both Chace (1940) and Guinot (1969) have acknowledged the difficulty involved in establishing the generic status of this species; however, in Chace's opinion P. nitida should be considered as belonging to the group of the Carcinoplacinae in which the genera Carcinoplax, Pilumnoplax, and Lithocheira are included.

Bathyplax typhla A. Milne Edwards 1880

Description.Rathbun, 1918, p. 19, text-fig. 4, pl. 2. Chace, 1940, p. 43.

Geographic range.North Carolina to Brazil; throughout the Gulf of México.

Bathymetric range. 294 to 874.4 m.

Material examined. G-766, 1 m, 1 f; G-659, 3 m, 2 f, 5 ovigerous f; G-694, 4 m, 6 f; G-666 1 ovigerous f; G-561, 3 f; G-362, 3 m, 1 f; G-998 5 m, 10 f; G-222, 20 m, 21 f, 9 ovigerous f; G-652, 31 m, 15 f, 8 j; G67, I f, 2 j; G-654 , I f; G-77, 1 f, 1 j; G-76, 1 f; G997, 1 m, 1 f; G-869, 1 m, I f; G-1099, 12 m, 17 f; G443, 2 m, 3 f, 1 ovigerous f; G-144, 3 m, 3 f, 23 j; G439, 14 m, 11 f, 3 ovigerous f; G-131, 2 f; G- 131, 2 m, 3 f , .2 ovigerous f , 7 j; G-225, 1 m; G-152, 3 m, 2 f, 1 ovigerous f, 6 j; G-161, 2 f, 1 ovigerous f, 2 j; G-650, 6 m, 3 f; G-658, 1 ovigerous f; G-112, 3 m; G-472, 5 m, 5 f, 1 ovigerous f; G-175, 5 m, 2 f, 1 ovigerous f; G-146, 3 f, 1 ovigerous f, 1 j; G-142, 2 m; G-403, 1m; G-66, 3 m, 2 ovigerous f; G-116, 1 m; G-442, 1 j; G-265, 1 f; G-160, 1 m, 1 ovigerous f; G226, 7 m, 8 f, 1 ovigerous f; G-87, 1 m; G-99, I m; G474, 2 m; G-478, 1 f, 1 ovigerous f; G-365, 3 m, 5 f, 1 ovigerous f; G-366, 3 m, 1 j; G-970, 3 m, 1 f; G-830, 1 m, I f; G-966, 1 m, 1 f; G-967, 1 ovigerous f; G-870, 6 m, 6 f; G-999, 1 m; G-1098, 2 m, 1 ovigerous f; G1101, 1 f; G-475, 12 m, 9 f, 1 ovigerous f; G-93, 4 m, 1 ovigerous f; G-94, 1 m; G-917, I f.

Distributional analysis. B. typhla is the most common brachyuran in the GERDA collection, and the most abundant component of all the species contained in the present study (Tables 1 and 2). From 57 GERDA stations a total of 435 specimens was obtained in which males and females were found in almost equal proportion; nearly 20 % of the females were ovigerous. The coefficient of dispersion of this goneplacid (CD = 24) showed a considerable deviation from the significance level expected for a Poisson distribution, which is indicative of a strong aggregation tendency among its individuals.

The pattern of distribution of B. typhla is conspicuously confined to the continental side of the Straits where it appeared scattered almost homogeneously in all three sectors of this area including part of the Blake Plateau (Fig. 20). Worth noting here is the apparent absence of the species from the insular side, a fact that may well be a result of the substrate preferences of B. typhla; the rough and irregular features described by Hurleyet al, (1962) on the Pourtales Terrace and the western edge of the Bahama Bank are apparently avoided by this goneplacid. The records ofB. typhla were taken from the western end of the southern Straits, along the Pourtales Escarpment, the north side of Cay Sal Bank, the Miami Terrace, and the upper northern Straits; a single record of B. typhla was obtained within the Northwest Providence Channel.

The bathymetric range of the species extended from 315 to 824 m; however, by placing 95 % confidence limits on its population can be defined between 532 and 625 m.

Remarks. Earlier records of B. typhla in the Straits have been obtained by the OREGON south of Dry Tortugas and off the Marquesas Keys (OREGON stations 1018, 1019 and 1334). The species was first recorded from the outer shelf off North Carolina By Williamset al. (1968). According to Pequegnat (1970), B. typhla represents the most abundant deep-sea brachyuran in the Gulf of México, though its population density is not considerable.

Ecological note. The type of substrate and the temperature conditions prevailing in the Straits are the two environmental variables that seem to govern the distribution of B. typhla.During the identification phase of the present study, many of the indivuduals examined had the dorsal surface of the carapace, and sometimes the legs, covered with a fine layer of a whitish sediment indicative of the muddy habitat in which this species dwells. This was later corroborated by the substrate data compiled for each locality where B. typhla occurred; such a substrate preference makes this goneplacid crab an excellent indicator of poorly consolidated bottoms composed of mud, pteropod ooze, and fine sand; combined with these three elements, there was other less frequent substrate material such as rock fragments, silt, finely fragmentated shells, and echinoid tests.

Fig. 20. Distributional pattern of Bathyplax typhla collected by the GERDA

On the other hand, there seems to be a significant correlation between the depth level at which the 10°C isotherm occurs throughout the Straits and vertical distribution of B. typhla. This isotherm constitutes an effective borderline for the upper dispersion of this goneplacid whose thermal range requires waters colder than 10°C.

In addition to being the commonest deepwater brachyuran in the Straits, B. typhla should at least be recognized as a subdominant component in the soft-bottom community that inhabits the upper slope region of this area. Among the important groups of macroinvertebrates integrating such community, one could mention the ophiuroids, echinoids, crinoids, alcyonarians, and the penaeid shrimpPleoticus robustus.

Geryon quinquedens Smith, 1879

Description. Rathbun, 1937, p. 271, (note pis. 85-96). Chace, 1940, p. 38 (key).

Geographic range. In the Western Atlantic from Nova Scotia to Brazil; Gulf of Mexico except southwestern quadrant.

Bathymetric range. 366 to 1695 m.

Material examined. G-964, I m; G- 1107, 1 j; G443. 1 m, 4 f, 2 j; G-127, 1 m, 2 f; G-448, 1 f, 1 j; G144. 1 m, 5 j; G-122, 2 j; G-125, 1 m; G-128, 1 m; G131, 1 f; G-222, 1 m, 1 j; G-226, 3 j; G-368, 2 m, 3 j; G-370, 2 j; G-372, 2 m; G-375, 1 m; G-446, 1 m; G960, 1 f; G-860, 5 m, 2 f; G-858, 1 m, 1 f; G-1106, 3 j.

Distributional analysis. G. quinquedens occupies the fifth rank among the brachyurans most frequently captured by the GERDA, an it also represents the predominant element of the brachyuran community that inhabits the deeper sector of the Straits. From 21 GERDA station, a total of 54 specimens was obtained, the males being slightly predominant over the females; no ovigerous females appeared in the collection. Even though the coefficient of dispersion for this species (CD = 1.4) lies above the significance level expected for a Poisson distribution, it fails to reveal a strong aggregative pattern; the individuals of G. quinquedens probably tend to follow a rather random dispersion on the floor of the Straits. This fact seems substantiated by the photographs taken with either underwater cameras or submersibles of the floor of the northeastern coast of the United States (Heezen and Hollister, 1971; Grassle et al., 1975). The photographs often show isolated individuals of G. quinquedens assuming a defensive position.

The distribution of G. quinquedens includes the thalweg plain of both the south and central sectors of the Straits (Fig. 21). The records of this species extended from the northern coast of Cuba to the northwestern end of Cay Sal Bank at depths ranging from 700 to 1695 m; approximately 95 % of the individuals of G. quinquedens were captured at a depth of 550 fm (1006 m) which almost concides with the population center calculated by Pequegnat (1970) for this species in the Gulf of Mexico.

Ecological note. In its northern geographic range,G. quinquedens experiences a broad variation in its vertical dispersion along the continental slope. According the the investigations conducted by Wigley et al. (1972), this species may occur at depths as shallow as 21 m (115 fm) in the Gulf of Maine and descends as deep as 2155 m (1178 fm). Nevertheless, this deep-water crab has essentially been considered as a bathybenthic component. In the Straits of Florida the confinement of G. quinquedens to thethalweg plain of the southern and central sectors seems to be more a result of the restricted depth range of the species than a reflection of its substrate requirements or temperature tolerance. The majority of the records obtained exhibited a thermal range from 7ºC to about 5ºC; except for the much shoaler depth of the northern Straits the temperature conditions and the bottom materials found in this region are somewhat similar to those of the southern sector, thus suggesting that perhaps the absence ofG. quinquedens from the former region may well be the result of the interaction of biotic factors such as competition, feeding habits, or predation. judging by the substrate data obtained and the group of macroinvertebrates that co-occurred with G. quinquedens, its habitat can be described as one composed of fine sediments, primarily mud and pteropod ooze, and integrated by a predominately echinoderm fauna (ophiuroids-asteroids) complemented with alcyonarians, solitary corals, sponges, and deep-sea penaeid shrimps.

Geryon fenneri Manning and Holthuis, 1984

Description. Rathbun, 1937, p. 271 (part), not pls. 85-86 Chace, 1940, p. 39 (key).

Geographic range.Western Atlantic: Chasepeake Bay, to Straits of Florida; Eastern Gulf of México.

Bathymetric range. 375 to 2002 m.

Material examined. G-766, 1 f; G-968, 1 f, 1 ovigerous f; G-1340, 3 m, 1 f; G-840, 1 m; G-997, 2 j; G-161, 1 m; G-160, 1 m; G-289, 2 m, 1 f; G-998, 1 m; G-839, 1 m; G-849, 1 m; G-483, 1 m, 1 f; G-175, 2 m; G-266, 1 f.

Distributional analysis. G. fenneri is another common element of the brachyuran community that occupies the upper continental slope of the Straits. The species appeared regularly throughout the GERDA collection, though not as frequent nor as numerous as its sympatric relative G. quinquedens. From 14 GERDA stations, a total of 23 specimens were identified, having a sex ratio of 2:1 in favor of the males; only one ovigerous female was recovered.

The coefficient of dispersion of this species (CD = 2. 1) departed from the unity value expected for a random type of spatial dispersion.

Fig. 21. Distributional pattern of Geryon quinquedens collected by the GERDA

The distributional pattern of G. fenneri is confined to the continental side of the Straits, occurring at the western end of the southern Straits, the Pourtales and the Miami Terraces, and on the upper part of the northern Straits (Fig. 22).

The bathymetric range of G. fenneri is defined between the depths of 322 and 470 m, attaining its optimum depth at about 396 m.

Ecological note. In the Western Atlantic,G. fenneri is said to have a more southerly distribution though occasionally it is captured by commercial boats fishing for deep-sea red crabs in the southern New England waters (Wingley et al1972). The accepted northest range for the species is set in the offing of Chesapeake Bay (Schroeder, 1959).

Depthwise,G. fenneri occupies a shoaler hábitat in comparison whit its congeneric species G. quinquedens rarely overlapping each other; consequently, this species cannot only be distinguished by the morphological characters described by Chace (1940) but also on the basis of the allopatric condition of their respective bathymetric dispersion in the Straits. The reduced depth range of G. fenneri may account to a certain degree for its absence from the insular side of the study area; the steepness of the insular slope sensibly reduced the niche availability for some of the brachyuran species included here.

Fig. 22. Distributional pattern of Geryon fenneri collected by the GERDA

The substrate data available for this species indicated the existence of a soft bottom composed of mud, sand and pteropod shells. G. fenneri unlike G. quinquedens, seems to enjoy a broader thermal range that extends from 15ºC to approximately 6ºC; however, it should be pointed out that, with the exclusión of the records obtained on the Pourtales Terrace, nearly all the recoveries of G. fenneriwere made below the 10°C isotherm.

Palicus gracilipes (A. Milne Edwards, 1880)

Description. Cympolia gracilipes, Rathbun, 1918,b, p. 221, text-fig. 133, pl. 52, figs. 3-4.

Geographic range. Straits of Florida; north coast of Cuba; Yucatan Bank; Grenada.

Bathymetric range. 112 to 545 m.

Material examined. G-924, 2 f; G-877, 1 ovigerous f; G-1328, 1 ovigerous f; G-4, 3 f.

Distributional analysis. This palicid crab occurred occasionally among the brachyurans dredged by the GERDA in th Straits of Florida; just 7 females especimens, two of wich ovigerous, were captured from the following three localities: upper slope off Miami, northeastern corner of Cay Sal Bank, and a locality within the Northwest Providence Channel east of Great Isaac Light. These records were taken at depths ranging from 216 down to 300 m.

Rathbun (1918) had listed a single male specimen of P. gracilipes from an ALBATROSS station simply reported as situated in the Bahamas; since then, no other records were known in the area of the Straits. In 1940, Chace reported this species for the first time from an ATLANTIS station located in the Old Bahama Channel off the northern coast of Cuba at a depth of 180 fm (329 m). In spite of the scarcity of our records, it is interesting to note that P.gracilipes, regardless of possible temperature and substrate differences, occurs at similar depth level on both the continental and insular margins of the Straits; Cuban inclusive.

Palicus sicus (A. Milne Edwards, 1880)

Description. Cymopolia sica, Rathbun, 1918b, p. 208, text-fig. 127, pl. 40, figs. 3-4.

Geographic range. From the eastern Gulf of Mexico through the Straits of Florida. North coast of Cuba. Winward Islands.

Bathymetric range. 28 to 622 m.

Material examined. G-1328, 1 m; G-482, 1 ovigerous f, G-274, 1 m, 2 f; G-134, 1 f; G-276, 1 m, 1 f; G-270, 1 m; G-390, 1 f; G-1099, 5 m, 2 f, 1 ovigerous f.

Distributional analysis. P. sicus is the most frequent and best represented, in terms of individuals per sample, of the seven species of palicid crabs obtained by the GERDA in the Straits. A total of 18 specimens were recovered having an almost equal ratio between males and females; only two ovigerous females were recorded. The coefficient of dispersion of P. sicus (CD = 4.6) deviated significantly from the unity value expected for a random dispersion.

P. sicus appeared distributed on both the continental and insular sides of the Straits. The species occurred on the upper slope south of Dry Tortugas, on the Pourtales Terrace, and then crossed to the western edge of the Bahama Bank near Sandy Cay, entered the Northwest Providence Channel, and continued northwards, onto the Little Bahama Bank.

The records of this species were taken from the edge of the continental shelf at about 191 m down to a maximum depth of 622 m; however, 95 % of its population seems to be concentrated between the boundaries of the outer shelf and the crest of the of the continental slope.

Remarks. Previous records of P. sicus in the Straits have mainly been given from the area of Key West and the Pourtales Terrace as well (Rathbun, 1918).

Ecological note. The fact that P. sicusreaches its northest geographic range in the area of the Straits should be indicative of the critical effect of temperature on the distribution of this palacid crab. With the exception of a record taken in the southern Straits, all the captured of P. sicus were made in waters warmer than 14°C. In the foregoing pages, allusion has often been made to the isotherm tilt cross-stream of the Florida Current as a cause for the elimination of suitable habitats on the continental side for species with limited thermal range; the same circumstances seem also to suppress the dispersion of P. sicus onto the continental margin of the Straits, where the interception of the 14°C isotherm is quite shallow.

Palicus gracilis (Smith, 1883)

Description. Cympolia gracilis,Rathbun, 1918, p. 218, text fig. 132, pl. 50, pl. 51, fig. 1. Pequegnat, 1970, p. 195, fig. 6-11.

Geographic range. From off Marthas Vineyard, Mass., to off Curacao; Gulf of México.

Bathymetric range. 183 to 686 m.

Material examined. G-464, 4 m, 1 ovigerous f; G142, 1 f; G-469, 1 m; G-1098, 1 m; G-830, 1 ovigerous f; G- 1018, 1 m; G-968, 1 ovigerous f.

Distributional analysis. P. gracilis had a limited number of occurrences throughout the GERDA's operation in the Straits. From seven GERDA stations, just 11 specimens were recovered, males and females appearing in equal proportion; 3 ovigerous females were collected.

P. gracilis was distributed from the upper slope south of Dry Tortugas to the central Straits between the Pourtales Terrace and the northern Cay Sal Bank; it also occurred at the Santaren Channel and on the Miami Terrace. The vertical distribution of this palicid crab along the Florida side appeared well defined along the 200 fm contour (366 m) whereas towards the Cay Sal Bank area the species descended to a deeper level, reaching its maximum depth range at 375 fm (696 m) near the northern coast of Cuba (Chace, 1940).

Remarks. Prior to this study, P. gracilis had been reported on two occasions by the ALBATROSS off Cape Florida from a depth of 200 fm (166 m).

Pequegnat (1970) in his study of the deepwater brachyuran crabs of the Gulf of Mexico has offered some interesting observations concerning the form and function of the walking legs of P. gracilis, which present a great disparity in lenght. He suggested the possibility that as the second pair of legs were twice as long as the first and third ambulatory legs, they might be employed to perform a sort of natatory locomotion.

Palicus dentatits (A. Milne Edwards, 1880)

Description. Milne Edwards and Bouvier, 1902, p. 53, pl. 9, figs. 15-17, pl. 10, figs. 1-6, pl. 11, figs. 1-3 Cymopolia dentata, Rathbun, 1918, p. 202, text-fig. 124.

Geographic range. Straits of Florida; easternmost part of the Gulf of México to Barbados.

Bathymetric range. 28 to 481 m.

Material examined. G-837, 1 ovigerous f; G-464, 1 ovigerous f; G-579, 1 m.

Distributional analysis. This is a rare species of palacid with a very limited number of records throughout its geographic range. The GERDA collection in the Straits yielded only three specimens of P. dentatus, two of which were ovigerous females. These three records were obtained from the Pourtales Terrace and the western end of the southern Straits south of Dry Tortugas at depths ranging from 174 to 363 m.

The only previous record of P. dentatus in the Straits was that given by Rathbun (1918) from a locality near Key West.

Palicus cursor (A. Milne Edwards, 1880)

Description. Cymopolia cursor. Rathbun, 1918, p. 215, textfigs. 130, 131, pl. 52, figs. 1-2.

Geographic range. Off Cape Hatteras, N.C.: Straits of Florida; north and south of Cuba; Gulf of Mexico to Barbados.

Bathymetric range. 185 to 650 m

Material examined. G-435, 1 ovigerous f; G-857, 1 ovigerous f; G-1085, 1 f; G-968, 1 f, 1 ovigerous f; G1323, 1 f.

Distributional analysis. P. cursor was poorly represented in the GERDA collection. Only six female specimens were collected from five localities in the Straits, three of which were situated south of the Marquesas Keys, one at the northern end off Key Largo, and another at the southwestern corner of the Little Bahama Bank. The bathymetric range of the species along the continental margin of the Straits is essentially confined to the transitional area between the outer shelf and the crest of the continental slope; on the insular side, P. cursor appeared to favor depths below the 200 fm contour (366 m), attaining its maximum depth range at about 650 m.

Remarks. Previous records ofP. cursor in the area of the Straits were limited to that given by Rathbun (1918) from the outer shelf near Key West. It is interesting to note the high incidence of ovigerous females in most of the existing reports of P. cursor obtained in the Gulf of México (Soto, 1972), the coast of Cuba (Chace, 1940), and the Straits of Florida as well.

Palicus floridanus (Rathbun, 1918)

Description. Cymopolia floridana, Rathbun, 1918, p. 220, pl. 41, figs. 3-4.

Geographic range.Straits of Florida; North coast of Cuba.

Bathymetric range. 190 to 476 m.

Material examined. G-828, 1 m, G-67, 1 m; G-857, 1 m; G-968, 1 m.

Distributional analysis. P. floridanus is one of the few species of deep-water brachyuran crabs whose geographic range seems somehow restricted to the area comprised between the Straits and the northeastern coast of Cuba. This palicid ocurred in limited number in two localities on the continental side of the southern and lower part of the northern Straits; a single record was taken from the upper slope south of the Marquesas Keys and another off Biscayne Bay at depths ranging from 190 to 355 m.

The only previous record of this species in the Straits was that of the holotype described by Rathbun (1918) from a locality off Sand Key.

Palicus depressus (Rathbun, 1897)

Description. Cymopolia depressa, Rathbun, 1918, p. 212, textfig. 128.

Geographic range.Straits of Florida; north coast of Cuba, and Lesser Antilles (off St. Croix off Dominica, and off Barbados).

Bathymetric range.103 to 463 m.

Material examined. G-133, 1 ovigerous f; G-233, 1 f; G-234, 1 ovigerous f; G-238, 1 ovigerous f; G-272, 1 m, 1 f, 2 ovigerous f.

Distributional analysis. There were only occasional occurrances of this species in the GERDA collection. From five GERDA stations eight individuals, predominantly ovigerous females were recoverd from the following localities in the Straits: the Pourtales Terrace at a depth of 190 m and the western edge of the Great Bahama Bank between Bimini and Riding Rocks close to the 200 fm isobath (366 m). These records extended the geographic range of the species from its previous northern range off Punta Alegre in the Old Bahama Channel (Chace, 1940).

Euchirograpsus antillensis Türkay, 1975

Description. Türkay, 1975

Geographic range. Straits of Florida and Antillean region.

Bathymetric range. 192 to 366 m.

Material examined. G-503, 1 m; G-480, 1 m.

Distributional analysis. The only records of thes recently described species obtained by the GERDA came from the Pourtales Terrace and the southwestern corner of the Little Bahama Bank at depths of 192 and 364 m, respectively. Both of these records were kindly made available to the writer by Dr. Türkay prior to the description of the species.

Euchirograpsus americanus A. Milne Edwards, 1880

Description. Rathbun, 1918, p. 282, text-fig. 144, pl. 74. Milne Edwards and Bouvier, 1923, p. 351, pl. 9, figs. 5-7.

Geographic range. From off Oregon Inlet, N.C., to the Caribbean Sea.

Bathymetric range. 31 to 509 m.

Material examined. G-234, 1 f; G-388, 1 m; G-510, 1 m; G-697, 1 m; G-232, 1 f; G-713, 1 f; G-387, 1 m; G276, 1 ovigerous f; G-837, 1 f.

Distributional analysis. E. americanus was a relatively common species during the GERDA survey of the Straits though seldom more than a single individual was taken at each haul; the collection included 4 males and 5 females, one of them gravid. Although the coefficient of dispersion of E. americanus (CD = 0.97) indicated a random type of spatial dispersion, it is difficult to place any confidence limit on such a value in view of the reduced number of individuals obtained.

E. americanus was found distributed on the insular side of the Straits and occurred only once on the Purtales Terrace (Fig. 23). The records from the Bahama side were obtained from off Sandy Cay, Bimini, and off Great Isaac Light; three additional records were from the southwestern and northwestern end of the Little Bahama Bank.

The bathymetric range of this grapsid crab along the continental side of the Straits is probably restricted to the shelf region, whereas on the insular margin, the species appeared concentrated near the 200 fm contour (366 m); the center of its population was estimated to lie at about 330 m.

Remarks. This species was first reported in the Straits from a FISH HAWK station (7511) made on the inner continental shelf off Cape Florida (fide Rathbun, 1918); another record was provided from an OREGON station (1005) located in the Santaren Channel, at a depth of 250 fm (458 m). E. americanus is known to occur on both the north and south coast of Cuba at similar depths as those given above for the Bahamas side.

Previously, E. americanus was thought to have a wider geographic distribution which includes the Eastern Atlantic and the Pacific. However, after the world-wide revision of the genus Euchirograpsus made by Türkay (personal communication) E. americanus has become, together with its congeneric species E. antillensis, restricted to the Tropical Western Atlantic.

Ecological note. The marked insularity in the occurrence of E. americanus and its conspicuous absence from the continental side at depths in excess of 200 m is probably caused by the compression of the isotherms on the Florida side of the Straits. This species tends to remain in waters than 10°C, roughly between 14 and 12°C; such temperature condition are usually found within the shelf environment.

Fig. 23. Distributional pattern of Euchirograpsus americanus collected by the GERDA

Although the substrate information gathered for this species was rather limited, there seems to be a significant incidence of E. americanus and hard substrates made up of coral rubble, rocks and shell fragments.

Achaeopsis thomsoni (Norman, 1873)

Descriprion. Rathbun, 1925, p. 29, text-fig. 7a, b, pl. 10.

Geographic range. Western Atlantic from Nantucket Shoals to Grenada; Eastern Atlantic from Faroe Islands to Cape Verde; Mediterranean; Gough Islands, South Atlantic; Agulhas Bank, near Cape of Good Hope; Indian Ocean; West and South Pacific Ocean; South Australia.

Bathymetric range. 111 to 2081 m.

Material examined. G-62, 1 f.

Distributional analysis. The single record of this rare species was obtained from a haul made by the GERDA off Biscayne Bay in 394 m. This is the second report of A. thomsoniin the area of the Straits. The species was first captured in 1893, during the Iowa State University Expedition, at the western end of the Pourtales Terrace.

The conspecificity of the Eastern Atlantic species with the forms that occur in the Indian Ocean and the Western Atlantic is considered doubtful by Monod (1956) and Guinot (1966).

Anomalothir frontalis (A. Milne Edwards, 1879)

Description. Rathbun, 1925, p. 25, pl. 8, fig. 1; pl. 9, fig. 1, pl. 207.

Geographic range.Straits of Florida; north coast of Cuba Montserrat; Guadeloupe; Barbados.

Bathymetric range. 134 to 421 m.

Material examined. G-239, 1 m; G-360, 1 m.

Distributional analysis. The only records of A. frontalis were obtained from the upper edge of the Pourtales Terrace south of Key West and the insular slope off Riding Rocks. These records extended their range into the Straits proper.

Anomalothir furcillatus (Stimpson, 1871)

Description. Rathbun, 1925, p. 24, pl. 8, pl. 9, fig. 2, pl. fig. 8, 206.

Geographic range. Off Cape Lookout, N. C., through Gulf of México, and West Indies to Grenada.

Bathymetric range. 55 to 773 m.

Material examined. G-837, 1 f; G-974, 1 m; G-972, 1 m, 1 f, 1 j; G-1009, I f; G-1102, 1 m; G-533, 1 f; G-598, 1 m; G-1327 1 f; G-1312, 61 m, 11 f, 23 ovigerous f; G-232, 2 m, 2 f; G-126, 1 m; G-251, 1 m; G-480, 1 m; G-233, 1 m.

Distributional analysis. A. furcillatus was a fairly frequent component among the brachyurans captured by the GERDA in the Straits; usually no more than a single individual was taken at each haul; however, there was an instance in which as many as 95 were captured from only one locality, which made the species the second most abundant element in the entire GERDA collection (Table 2). A total of 113 specimens were obtained from 14 GERDA stations located on both the continental and insular margins of the Straits. The males were predominant over the females by roughly a 2:1 ratio; nearly 50 % of the females were in ovigerous stages. In view of the large number of specimens recorded from a single locality the coefficient of dispersion of this species (CD = 78) experiences a strong deviation from the unity value expected for a Poisson distribution.

A. furcillatus appeared distributed in the central Straits along the Pourtales Terrace and at the eastern side of Cay Sal Bank; on the insular margin the species occurred off Bimini, east of the Great Isaac Light, and at the southwestern corner and northern side of the Little Bahama Bank (Fig. 24).

A depth range of A. furcillatus on the continental side of the Straits is restricted to the up permost part of the slope at depths ranging from 183 to 265 m; this species was captured only once at 773 m, which is the maximum depth record ed for this majid crabs. Its vertical dispersion I along the insular slope is clearly delineated at about the 200 fm isobath (366 m).

Remarks. The previous records of A. furcillatus in the area of the Straits were limited to the upper slope off Dry Tortugas and Key West (Rathbun, 1925).

Ecological note. The two major factors that seem to condition the dispersion of A. furcillatus in the Straits are the substrate and its aparent limited thermal range. The substrate data available for the species indicated a marked preference for hard rocky bottoms such as those known to exist on the Pourtales Terrace and along the insular slope (Hurley et al., 1962; Staiger, 1970). The predominant bottom material recognized in the localities where A. furcillatus occurred were rocks, coral rubble, sand/shell fragments, and pteropod tests. Worth noting is the fact that in both the continental and insular biotopes occupied by the especies, the benthic community was apparently integrated by similar assemblages of macroinvertebrates, consiting mainly of alcyonarians, sponges, echinoids, crinoids, and ophiuroids.

In sprite of the discrepancy observed in the bathymetric range ofA. furcillatus on both sides of the Straits, no significant difference in its thermal range was detected. The species tends to remain well above the 100C isotherm at temperatures fluctuating between 13 and 16°C. There was only one instance in which a single specimen was recovered near the Pourtales Escarpment at a depth level (773 m) where temperature is presumably colder than 10°C; however, the depth of capture of this particular records seems excessive for this species whose maximum depth range is 480 M.

Pyromaia arachna Rathbun, 1924

Description. Rathbun, 1925, p. 131, pls. 42, 43.

Geographic range. South Carolina to the Gulf of México.

Fig. 24. Distributional pattern of Anomalothir furcillatus collected by the GERDA

Bathymetric range. 183 to 384 m.

Material examined. G-460, I m, 2 j; G-467, 1 m.

Distributional analysis. P. arachna is a rather rare inhabitant of the Straits whose occurrence in the GERDA collection was limited to two records taken in the southern Straits from the upper slope south of Dry Tortugas in 227 and 359 m. Even though the geographic range of P. arachna extends as far north as the outer shelf off South Carolina (ALBATROSS station 10035), presently no other records are known of this majid along the Southeastern Coast of the United States. Conversely, the species seems indigenous to the Gulf of MExico where it constitutes a common element of the brachyuran fauna inhabiting the outer shelf of the northeastern region (Soto, 1972). The especies: has also been captured by the OREGON (station 1005) in the proximity of the southern Straits at a similar depth as that of the GERDA records.

Pyromaia cuspidata Stimpson, 1871

Description. Rathbun, 1925, p. 129, text-fig. 49, pl. 41 Williams, 1965, p. 240, fig. 216.

Geographic range. Off Cape Lookout, N.C., to Eastern Gulf of Mexico, Yucatan Channel; Cuba.

Bathymetric range. 28 to 622 m.

Material examined. G-842, 3 f; G-757, 7 m, 2 f; G-712, 1 m; G-1099, 1 f; G-413, 1 m; G-605, 1 f; G-173, 1 m; G-507, 1 m, 1 f; G-626, 2 m, 2 f; G-110, 1 m, 3 f; G-935, 1 m; G-1327, 2 f; G-1206, 1 m; G- 1329, 1 m; G-275, 2 m; G-238, 5 m, 5 f; G-251, 1 m; G-432, 5 f; G-452, 2 m, 3 f; G-459, 4 m; G-460, 1 m, 1 ovigerous f; G-462, 7 m; 1 f; G-480, 1 f.

Distributional analysis. P. cuspidata ranks fouth among the ten most frequent species of deep-water brachyurans found in the Straits of Florida; its relative abundance is only second to that of the most abundant majid crab, A. Furcillatus (Tables 1 and 2). From 23 GERDA stations, a total of 70 specimens was recovered, the males being slightly perdominant over the females; only one ovigerous female was recovered. The spatial dispersion of P. cuspidata seems to follow a clustering pattern as indicated by the significant deviation of its coefficient of dispersion (CD = 5.2) from the value expected for a random distribution.

P. cuspidata showed a nearly ubiquitous dispersion throughout the Straits (Fig. 25). The species appeared scattered along the upper slope of both the continental and insular margins of this area. Records from the former region were taken in the area south of Dry Torutugas, the Pourtales Terrace, the lower end of the northern Straits, off Fort Lauderdale, and off the St. Lucie Inlet; from the insular region, the records came from the northwestern corner of the Great Bahama Bank starting off Riding Rocks through the entrance of the Northwest Providence Channel; the remaining records were recovered along the western edge of the Little Bahama Bank.

Fig. 25. Distributional pattern of Pyromaia cuspidata collected by the GERDA

P. cuspidata is essentially an inhabitant of the transitional region between the outer shelf and the upper continental slope of the Straits; throughout the GERDA collection this species exhibited a well defined bathymetric range extending between 174 and 622 m; however, 95% of its population is centered around 290 m.

Remarks.A considerable number of records of P. cuspidatawere obtained during the early explorations of the Straits (FISH HAWK, BACHE, BLAKE, etc.), particularly from the southern and central sectors of the area; most of these findings were made within the limits of the outer shelf and the slope's crest. Additional records of this species have been provided by the exploratory fishing vessels OREGON and COMBAT from the insular margin off Ridign Rocks and Orange Cay (COMBAT stations 445, 447), the northern end of Little Bahama Bank (COMBAT station 235), and the Nicholas Channel (OREGON station 1345). The ATLANTIS expedition yielded a number of records ofP. cuspidata from the south and north coast of Cuba, particularly along the Old Bahama Channel (Chace, 1940).

Ecological note. The dispersion of the species in the area of study seems mainly governed by the interaction of depth and temperature rather than the type of substrate. According to Williams (1965) P. cuspidata is able to settle in a wide variety of bottom types which include mud, sand, pebble, and broken coral. All the recoveries of this species made by the GERDA were taken at depths well above the 10°C isotherm.

Collodes robustus Smith, 1881

Description.Rathbun, 1925, p. 114, text-figs. 36, 37, 38, 40, 41, pl. 29.

Geographic range. South of Nantucket, Mass.; off Cape Hatteras, N. C.; Straits of Florida; Southern Caribbean.

Bathymetric range. 90 to 683 m.

Material examined.G-413, 1 ovigerous f; G-681, 1 m; G-624, 1 m.

Distributional analysis. The captures ofC. robustus in the Straits were made on the outer shelf near Boca Raton Inlet, north of Bimini, in the Northwest Providence Channel east of the Berry Islands at depths ranging from 183 to 225 m; these are the first records of this species for the area of the Straits. At present, C. robustus is known to occur as far south as the southeastern Caribbean region near the Panama Canal area (Holthuis In: Bayeret al., 1970).

Sphenocarcinus corrosus Milne Edwards, 1875

Description. Williams, 1965, p. 248, fig. 227.

Geographic range. Off Cape Lookout, N.C., to Barbados.

Bathymetric range. 165 to 302 m.

Material examined. G-239, I f.

Distributional analysis. The single occurrence of S. corrosus was obtained from the insular side of the Straits off Riding Rocks in 302 m. On the continental side, this species is probably restricted to the shelf habitat, seldom extending its range beyond the 100 fm contour (183 m). The early examination of the GERDA collection yielded female specimens of S. corrosus taken of Key Largo at 82 m and east of Key West at a depth of 145 m. Rathbun (1925) had previously reported a single female specimen of this species from off Sandy Key, in 165 m.

Stenocionops spinosissima (Saussure, 1857)

Description.Rathbun, 1925, p. 455, pl. 165, fig. 2, pl. 264, figs. 34, pl. 265.

Geographic range. Off North Carolina; Southern Florida, Gulf of Mexico; North Coast of Cuba; Haiti; West Indies to Rio de Janeiro, Brazil

Bathymetric range. 48 to 549 m.

Material examined. G-234, 1 m; G- 168, 1 carapace; G-223, 1 m; G-510, 1 m.

Distributional analysis. A limited number of specimens of this majid crab were collected by the GERDA along the western edge of the Bahamas Bank from off Bimini and the Great Isaac Light to the Little Bahama Bank; all these re cords were taken from the upper slope at depths ranging from 252 to 463 in.

The only record of S. spinosissima on the continental side of the Straits was obtained during the BACHE expedition off Sombrero Key at about 99 m; an additional report has been given by the COMBAT from the insular side of the Straits off Orange Cay at a maximum depth of 549 in.

Ecological note. The distribution of this species throughout the Straits seems more affected by the temperature and substrate conditions prevailing in the area than by depth. S. spinosissima possesses a broad bathymetric range that enables it to inhabit both the shelf and slope environments though allegedly its center of distribution appears to be quite shallow, between 110 and 183 m, (Pequegnat, 1970); obviously, the optimum insular depth for this species is substantially deeper (366 in) as the records given inhere attest as well as those obtained by the ATLANTIS on the north coast of Cuba (Chace, 1940)

On the insular margin of the Straits, S. spinosissima always maintains a depth level above the 10°C isotherm showing a thermal range between 12 and 15°C. Therefore, it is reasonable to assume that due to the shoaling of the referred isotherm along the continental margin, the vertical dispersion of the species is restricted to the area adjacent to the outer shelf.

Anasimus fugax A. Milne Edwards, 1880

Description. Rathbun, 1925, p. 64, pl. 23, figs. 5-6, pl. 211.

Geographic range. Straits of Florida; Puerto Rico to Cape Frio Brazil.

Bathymetric range. 64 to 330 m.

Material examined. G-251, 1 m, 1 ovigerous f; G-637, 1 m; G-239, 1 ovigerous f; G-274, 1 ovigerous f.

Distributional analysis. This uncommon species occurred at four GERDA stations located at the northwestern corner of the Great Bahama Bank from off Riding Rocks to Great Isaac Light and at the northern side of the Little Bahama Bank; only five specimens were captured of which three were ovigerous stages. Most of these records were taken from the upper slope at depths ranging from 183 to 330 in. These are the first findings of A. fugax in the Straits.

Stenorhynchus seticornis (Herbst, 1788)

Description. Rathbun, 1925, p. 13, fig. 3, pls. 2-3. Williams, 1965, p. 244, figs. 222, 223 K.

Geographic range. North Carolina to Rio de Janeiro, Brazil; Bermuda; Eastern Atlantic from Madeira and Canary Islands to Angola.

Bathymetric range. Near surface to 1490 in.

Material examined. G-274, 2 m; G-276, 2 m; G-509, 4 m; G-493, 1 m.

Distributional analysis. The limited number of occurrences of this species was obtained from the insular margin of the Straits near the northwestern corner of the Great Bahama Bank and the southern end of the Little Bahama; these records were at depths close to the 200 fm isobath (366 m). According to Yang (1976), the comparative study of the larval characters of the shallow and deep-water population of S. seticornis in the Western Atlantic provided sufficient evidence to warrant the recognition of a distinct species ofStenorhynchus. The population ofStenorhynchus sp. presumably occupies the former deep range of the arrow crab S. seticornis.

Podochela curvirostris (A. Milne Edwards, 1879)

Description. Rathbun, 1925, p. 50, pls. 19, 210.

Geographic range. Straits of Florida; north coast of Cuba; Yucatan Channel to Barbados and Grenadines.

Bathymetric range. 134 to 384 m.

Material examined. G-924, 1 ovigerous f; G-925, 1 m; G-480, 1 f; G-493, 1 m; G-692, 1 f; G- 1329, 3 m, 1 ovigerous f; G-251, 2 m, 3 ovigerous f; G-390, 1 ovigerous f.

Distributional analysis. This species appeared with certain frequency throughout the GERDA collection; however only a limited number of specimens was obtained. From eight GERDA stations, a total of 15 individuals was identified, males and females occurring in almost equal proportion; six of the females were ovigerous stages. According to its coefficient of dispersion (CD = 3. 1), the species adopts an aggregative spatial pattern of distribution.

P. curvirostris was mainly distributed in the insular margin of the Straits, occurring within the Northwest Providence Channel east of the Great Isaac Light and along the southern and northern end of the Little Bahama Bank (Fig. 26). A single occurrence of this species was recorded from the surface of the Pourtales Terrace.

The depth range of the species extended from 192 to 448 m, attaining its optimum depth at about 310 m.

Remarks. Prior to the present study, the ALBATROSS (stations 2167 and 2337) and the BLAKE (station 65) had captured P. curvirostris from the southern Straits off Havana, Cuba; subsequently, the COMBAT dredged this species from a locality at the northern end of the Little Bahama Bank, which presently constitutes the northest limit for this majid.

Euprognatha rastellifera marthae Rathbun, 1925

Description. Rathbun, 1925, p. 96, text-fig. 30, pl. 33, pl. 34, figs. 1-2, pl. 35, figs. 3-4, pl. 216. Williams, 1965 p. 237, fig. 213.

Geographic range. Off George Banks to Straits of Florida.

Bathymetric range. 81 to 502 m.

Material examined. G-635, 1 m; G-482, 1 ovigerous f; G-238, 1 ovigerous f; G-676, 1 carapace; G-757, 1 ovigerous f.

Fig. 26. Distributional pattern of Podochela curvirostris collected by the GERDA

Distributional analysis. Only six specimens of the northern subspecies E. r. marthae were identified from six GERDA stations located on both margins of the Straits. The records were taken from the Pourtales Terrace, the outer shelf off Lake Worth, the northwestern corner of the Great Bahama Bank, and the northern end of the Little Bahama Bank (Fig. 27).

The bathymetric range of this subspecies on the Florida side seems resticted to the outer shelf whereas on the insular side its depth range is perhaps delineated close to the 200 fm isobath (366 m).

Remarks. The taxonomic validity of this subspecies has been questioned by Williams (1965) in view of the considerable geographic overlapping of the two subspecies involved, a fact that can not be admitted under normal conditions. The GERDA specimens displayed a certain degree of variation in the characters that separate E. r. marthae from E. r. actua, which sometimes made their identification difficult. It is obvious that this problem deserves further study.

Euprognatha rastillifera acuta A. Milne Edwards, 1880

Description. Rathbun, 1925, p. 96, pl. 34, figs. 1-2.

Geographic range. Straits of Florida; north coast of Cuba to Grenada and Barbados.

Bathymetric range. 28 to 708 m.

Fig. 27 Distributional pattern of Euprognatha rastellifera marthae collected by the GERDA

Material examined. G-974, 1 ovigerous f; G-986, 1 ovigerous f; G-1099, 1 ovigerous f; G-666, 1 m; G915, 1 m; G-1312, 1 m.

Distributional analysis. The records of the southern subspecies E. r. acuta were limited to only six stations made at six localities in the Straits: the upper slope south of Dry Tortugas, the Pourtales Terrace and Cay Sal Bank, the Northwest Providence Channel west of the Berry Islands, the southern corner of the Little Bahama, Bank, and the Blake Plateau. The depth range of E. r. acutaextended from 189 to 622 m.

Remarks.Although the distributional pattern of E. r. acuta is essentially compatible with that of E. r. marthae, there was a slight difference in their repective mean depth of occurence in the Straits. The former subspecies had a depth range sensibly deeper than that of the latter, particularly along the insular margin.

Rochinia tanneri (Smith, 1883)

Description. Rathbun, 1925, p. 216, pl. 227, fig. 1, Williams et al., 1968, p.

Geographic range. Off Marthas Vineyard, Mass., to Straits of Florida.

Bathymetric range. 128 to 351 m.

Material examined. G-67, 1 m; G-135, 1 f; G-432, 1 carapace.

Distributional analysis. The occurrences of this majid in the GERDA collections were limited to three records on the continental side of the Straits from the following localities; outer shelf south of the Marquesas Key, central portion of the Pourtales Terrace, and upper slope of Biscayne Bay. The depth range in these three localities fluctuated from 193 to 351 m.

The previous records of R. tanneri in the area of the Straits included those obtained by the FISH HAWK (stations 7279 and 7280) and by the Biological Expedition of the Iowa State University from the adjacent area to Key West; such records were taken primarily from the outer and upper slope región, and they represent the southern limit in the geographic range of R. tanneri.

Rochinia umbonata (Stimspon, 1871)

Description. Rathbun, 1925, p. 222, text-fig. 85, pl. 72, pl. 73 fig. 1.

Geographic range.Off North Carolina, through the Straits of Florida, to the northeastern Gulf of Mexico; West Indies.

Bathymetric range.161 to 915 m.

Material examined. G- 177, 1 m; G- 103, 1 m; G170, 1 f; G-91, 1 m; G-311, 1 f; G-386, 1 m.

Distributional analysis. R. umbonata is the only member of the Majidae capable of settling in the deep slope habitat of the Straits. Its occurrence throughout the GERDA collection was limited to six individual, four males and two females, from two well defined localities situated at both ends of the northern Straits (Fig. 28). Three of the records were taken from the thalweg plain of the lower and in about 824 m; the other three records were obtained at the upper end, at depths ranging from 604 to 686 m.

Remarks. This species had previously been captured in the área of the Straits by theFISH HAWK (station 7283 and 7286) from the upper slope off Key West and by the ATLANTIS in the proximity of the Nicholas Channel south of Cay Sal Bank.

Ecological note. The occurrence ofR. umbonata in the Straits appears closely associated with the rough and irregular bottoms that characterize the base of the insular slope. The substate data gathered for the biotope in the upper end of the northern Straits indicated the existence of a hard bottom covered with coral rubble material occupied by a diverse assemblage of macroinvertebrates such as alcyonarians, sponges, deepwater corals, crinoide, ophiurodis and echinoids. The substrate composition at the second locality between the area of Bimini and Riding Rocks included similar rubbly materials.

In addition to the substrate preferences of R. umbonata, this majid crab probably possesses a stenothermal condition that subordinates its vertical dispersion to waters colder than 10°C; most of the records secured of this species had temperatures of about 8°C.

Rochinia hystrix (Stimpson, 1871)

Description. Rathbun, 1925, p. 214, pl. 70, 71.

Geographic range. Northeastern Gulf of Mexico; Straits of Florida and Caribbean Sea as far as St. Vincent and Barbados.

Bathymetric range. 38 to 708 m.

Fig. 28. Distributional pattern of Rochinia umbonata collected by the GERDA

Material examined. G- 1125, 1 m; G-234, 6 m, 1 f; G-663, 1 m; G-635, 1 m; G-198, 1 m; G-666, 1 m; G-937, 1 m; G-911, 1 m; G-169, 1 f, G-233, 1 m; G-232, 1 j; G-132, 1 f; G-842, 1 m; G-1102, 1 f; G-909, 1 f; G-972, 1 m, 1 f; G-974, 1 j.

Distributional analysis. During the GERDA operation in the Straits, R. hystrix proved to be a fairly common species though seldom more than one specimen was recovered in each haul. According to its relative frequency of occurrence, R. hystrix ranked 8th among the ten most frequent brachyurans included in this study (Table 1). From 17 GERDA stations a total of 24 individuals were obtained in which the males outnumbered the females by a ratio of more than 3: 1; no ovigerous females were present in the collection. The computed coefficient of dispersion for this species (CD = 3.0) departed from the value expected for a random distribution thus suggesting a clustering type of spatial dispersion among its individuals.

This majid crab was found scattered on both the continental and insular margins of the Straits, also occurring on the Blake Plateau (Fig. 29). The localities where this species was captured included both the Pourtales and the Miami Terraces, the area off Bimini, the entrance of the Northwest Providence Channel, and the western edge of the Little Bahama Bank.

The bathymetric range of R. hystrix along the continental margin was mainly confined to the upper part of the slope at depths ranging from 179 to 329 m while on the insular its depth range was sensibly deeper, occurring between 415 and 573 m; the estimated center of the population of R. hystrix lies roughly at 414 m with 95 % of the individuals distributed between the 350 to 477 m depth interval.

Fig. 29. Distributional pattern of Rochinia hystrix collected by the GERDA

Remarks. The species was first recorded in the Straits by Rathbun (1926) from the upper slope of the area adjacent to Key West; subsequent records, have been provided by the exploratory fishing vessel OREGON and COMBAT from a locality southwest of Dry Tortugas, the Nicholas Channel, and off Orange Cay (OREGON stations 1342 and 1550; COMBAT station 447).

Ecological note. The somewhat limited depth range of R. hystrix and the substrate requirements of this majid are two of the factors that seem to influence its dispersion in the Straits. Even though most of the records of this species were made at deeph levels above the point on interception by the 10°C isotherm, R. hystrix is capable of penetrating this thermal boundary, occurring in areas where temperature conditions are colder than 8°C.

The population of R. hystrixin the Straits is primarily concentrated in localities in which the bottoms are particularly irregular and rough, such as those present on the Pourtales Terrace and along the insular slope. The substrate data available for this species indicated the predominance of rocky and shelly coral rubble materials combined occasionally with mun and sand.

Rochinia crassa (A. Milne Edwards, 1879)

Description. Rathbun, 1925, p. 210, text-fig. 83, 84, pl. 68,69,226.

Geographic range. From off Nantucket, Mass., to the Straits off Florida; northern coast of Cuba; Gulf of Mexico, except southwestern quadrant.

Bathymetric range. 128 to 732 m.

Material examined. G-998, 1 m, 3 j; G-62, 4 m; G21, 3 m; G-67, 1 m, 2 j; G-76, 1 m, 1 f, 4 j; G-77, 1 f, 5 j; G-161, 1 in; G-172, 1 m, 1 f; G-174, 1 m; G-288, 1 m 1 j; G-289, 1 j; G-299, 1 f; G-657, 1 m 1 f; G-659, 1 m; G-758, 1 m; G-607, I ovigerous f; G-857, 1 m, 1 f; G654, 1 m; G-1085, 1 f; G-655, 1 m.

Distributional analysis. R. crassa represented the second most important majid crab in the GERDA collection from the Straits. This species ranked 6th among the ten most common deepwater brachyurans included in this report, and 11 th according to its relative abundance (Tables 1 and 2). A total of 44 specimens were taken at 20 GERDA stations, the males being predominant over the females by a 2:5 ratio; a considerable number of juvenile forms were recorded, and only one ovigerous female was present. The coefficient of dispersion for the species (CD = 3.2) deviated from the unity value expected for a random distribution thus indicating a clustering types of spatial dispersion.

R. crassa was essentially distributed on the continental margin of the Straits from the southern sector to the upper end of the northern Straits (Fig. 30). This species is recorded from the outer shelf south of the Marquesas Keys, the Pourtales Escarpment, off Key Largo, the Miami Terrace, and particularly from the outer shelf and upper slope off the St. Lucie Inlet; the deepest record of R. crassa was recovered from a locality near the entrance to the Northwest Providence Channel.

R. crassa exhibited a fairly wide bathymetric range in the Straits that extended from about 180 m down to about 642 m; however, 95% of its population appeared concentrated at depths between 274 and 403 m.

Remarks. The records listed by Rathbun (1925) for R. crassa indicated its existence all along the upper slope region of the east coast of Florida, from off Fernandina southward to the Marquesas Keys.

Ecological note. The distribution of R. crassa along the upper slope of the continental margin of the Straits is probably dependent on the nature of the substratum and the normal depth range of this species. This deep-water crab appeared closely associated to bottoms composed of unconsolidated materials, mainly mud, fine sand, and pteropod tests, sometimes graded with shell fragments and echinoid tests. This particular substrate requirement, coupled with the defined depth range displayed by R. crassa, are perhaps the causes that suppress its dispersion onto the insular slope of the Straits. This species is known to occur on the northern coast of Cuba (Chace, 1940) at greater depths than elsewhere (577 to 1217 m) in the Straits; therefore, as in the case of other deep-water brachyurans, one would expect to find the same species inhabiting the western side of the Bahama Bank at a similar depth range. However, the expeditions conducted in the area of the Straits have failed to yield records of R. crassa from the Bahamas side proper.

Trachymaia cornuta A. Milne Edwards, 1880

Description. Rathbun, 1925, p. 229, text-fig. 87, pl. 80 pl. 232, figs. 3-5.

Geographic range. From the Little Bahama Bank to the north coast of Cuba; St. Thomas; St. Croix; Nevis; Barbados.

Bathymetric range. 150 to 619 m.

Material examined. G-925, 2 m; G-915, 2 f, 1 ovigerous f; G-935, 1 m, 1 f; G-1327, 1 ovigerous f, G-256, 2 m, 1 f; G-722, 1 j.

Distributional analysis. T. cornuta is one of the characteristic insular elements of the deep brachyuran community of the Straits. Only 12 specimens of this majid crab were obtained from six GERDA stations. Its distribution in the Straits was strictly confined to the insular margin occurring at the entrance of the Northwest Providence Channel, and along the northwestern corner of the Great Bahama Bank; two additional records were taken near the northeastern end of the Little Bahama Bank (Fig. 31).

Fig. 30. Distributional pattern of Rochinia crassa collected by the GERDA

The bathymetric range of T. cornuta appears restricted to depths between 392 and 480 m, attaining its optimum depth at about 438 m.

Remarks. Prior to this study, there were only two records of T. cornuta from the area adjacent to the Straits both of them obtained at the northern end of the Little Bahama Bank. The first record was from the ALBATROSS (station 2655), and the second one from the COMBAT (station 238) from a locality similar in position to that of two GERDA stations in which T. cornutawas captured.

Ecological note.The geographic range of T. cornuta in the Tropical Western Atlantic constitutes a fine example of the type of Antillean distribution adopted by some of the brachyuran species studied herein. These elements are usually dispersed over the entire Antillean Arc reaching their northest point of distribution in the vicinity of the Straits; in the case ofT. cornuta such limit corresponds to the Little Bahama Bank. The substrate data available for this species, though limited, indicated the presence of soft bottoms integrated by fine mud and pteropod shells; among the common macro-invertebrates associated with T. cornuta were ophiuroids, and spatangoids echinoids.

Fig. 31. Distributional pattern of Trachymaia cornuta collected by the GERDA

Nibilia antilocapra (Stimpson, 1871)

Description.Rathbun, 1925, p. 290, text-fig. 97, pls. 102 103, 239. Williams, 1965, p. 251, fig. 230.

Geographic range. Off Key Hatteras, N.C., to Gulf of Mexico just east of the Mississippi River delta, and Gulf of Campeche; Windward Island, West Indies.

Bathymetric range. 71 to 342 m.

Material examined. G-598, 1 m; G-133, 1 m; G-757, 1 f; G-835, 1 m; G-480, 2 m, 2 f, 1 ovigerous f; G-135, 2 m, 2 f, 2 ovigerous f; G-813, 1 f; G-845, 1 m; G-836, 1 m, 1 f; G-830, 1 f.

Distributional analysis. N. antilocapra was a common species throughout the GERDA collection in the Straits. From 10 GERDA stations, a total of 20 specimens were collected, the males and females occurring in almost equal proportion; only three ovigerous females were caught. The coefficient of dispersion of this majid (CD = 3.5) departed from the value expected for a random dispersion, such diviation is indicative of a clustering tendency among the individuals of the species.

The distributional pattern of N. antilocapra was entirely confined to the continental margin of the Straits, particularly to the central sector (Fig. 32). The records of this species were obtained from the upper border of the Pourtales Terrace, and on the surface of the Miami Terrace in depths of 183 to 342 m.

Remarks. Previous known records of N. antilcapra in the Straits were limited to those given by Stimpson (1871) from the type locality for the species: Carysfort Reef, and Alligator Reef.

Ecological note. The distribution of N. antilocapra in the Straits is probably subordinated first by the substrate configuration of this area and second by the limited bathymetric range of the species. N. antilocapra is normally found with in the shelf boundaries, seldom extending its range beyond the outer shelf. The conspicuous concentration of the records of N. antilocapra on the surface of the Pourtales Terrace is probably a result of the substrate preferences exhibited by this majid crab. All the recoveries of this species were made on predominantly rubbly and irregular bottoms. The substrate data obtained included the following materials: rocks, coral debris, sand and shell rubble, cinder, and Thalassiaremains; earlier records of N. antilocapra in the Straits have also been taken from coarse sand, broken shell and coral bottoms (Rathbun, 1925). The Pourtales Terrace, in this respect, seems to provide optimum habitat conditions not only to a number of brachyuran elements here included, but also to a large array of macro-invertebrates that compose the community in which the Porifera, alcyonarians, scleractinians, echinoids, asteroids, and ophiuroids are dominant elements.

Fig. 32. Distributional pattern of Nibilia antilocapra collected by the GERDA

Mesorhoea sexpinosa Stimpson, 1871

Description. Rathbun, 1925, p. 547, text-fig. 150, pl. 200.

Geographic range. Off North Carolina; Straits of Florida; Gulf of Mexico; Puerto Rico; Flannegan Passage.

Bathymetric range. 8 to 210 m.

Material examined. G-681, 1 m.

Distributional analysis. The single record of this parthenopid was obtained from the Northwest Providence Channel, west of the Berry Islands in 211 m. According to the earlier records ofM. sexpinosa in the Straits (Rathbun, 1925), the species is a normal component of the reef brachyuran fauna distributed along the Florida Keys, which rarely occurs beyond the inner shelf region. Williams et al., (1968) reported this small parthenopid for the first time from the continental shelf off North Carolina from a depth of 100 m.

Parthenope (Platylambrus) pourtalesii (Stimpson, 1871)

Description. Rathbun, 1925, p. 521, pls. 182, 183, 276. Williams, 1965, p. 268, fig. 248.

Geographic range. Off New Jersey to Grenada; southeastern quadrant of the Gulf of México.

Bathymetric range. 18 to 348 m.

Material examined. G-835, 1 ovigerous f; G-482, 2 m, 1 f , 3 j; G-842, 1 m; G-1036, 1 m, 1 ovigerous f; G-1099, 1 j; G-275, 1 f; G-757, 3 m 1 f; G-134, 1 j; G-432, 1 m; G-457, I j; G-452, 1 m, 2 f; G-480, 2 m, 1 f; G-239, 1 m; G-462, 1 m, 1 f; G-400, 1 f

Distributional analysis. P. pourtalesiirepresents a common component of the brachyuran community that inhabits the continental margin of the Straits, particularly the area encompased by the Pourtales Terrace. The species frequently occurred in the GERDA collection, having been captured at 15 stations from which a total of 30 specimens were obtained: the males appeared to be slightly predominant over the females; and only two ovigerous stages were recognized. The coefficient of dispersion computed for this parthenopid (CD = 3.0) lies above the expected value for a Poisson distribution, thus indicating the existence of an aggregative spatial pattern among its individuals.

P. pourtalessiwas found distributed in the southern and central sectors of the continental margin of the Straits as well as on the northwestern corner of the Great Bahama Bank and the Blake Plateau (Fig. 33). The records of this species were obtained from the outer shelf south of the Marquesas Keys and from the Pourtales Terrace; the insular records were recovered off Riding Rocks and the Great Isaac Light.

The bathymetric range of P. pourtalessi extended from 179 to 622 m; however, its population center is basically confined to the slope's crest in about 244 m.

Remarks. Previous reports of P. pourtalessi in the Straits have mainly been obtained from the outer shelf region off Fowey Rocks and the area near Key West (Rathbun, 1925). The species is also known to occur on the middle shelf region off Key Largo (COMBAT station 457).

Ecological note. P. pourtalessi is by far better represented in the GERDA collection than its sympatric relative P. agona. Even though there is a certain similarity in the habitat conditions required by these two species, they seem to exclude one another in the área of the Straits; both elements never occurred together in the same haul during the GERDA's operation. P. pourtalessi is more likely to be found in the transitional area between the outer shelf and the upper slope, whereas P. agonaprefers to settle in a much shallower habitat.

Parthenope (Parthenope) agona (Stimpson, 1871)

Description. Parthenope (Parthenope) agonus,Rathbun, 1925, p. 513, text-fig. 146, pls. 178-179, pl. 275, figs. 1-3.Parthenope (Parthenope) agona, Williams, 1965, p. 266, fig. 246.

Geographic range. Off Cape Hatteras and Lookout, N.C., through Straits of Florida; Gulf of Mexico, near Pensacola, Fla.; Puerto Rico; Trinidad; between British and Dutch Guiana.

Fig. 33. Distributional pattern of Parthenope pourtalesii collected by the GERDA

Bathymetric range. 46 to 392 m.

Material examined. G-681, 1 f; G-637, 1 m; G-624, 1 m; G-493, 2 m; G-397, 1 m, 1 ovigerous f.

Distributional analysis. Only seven specimens ofP. agona were captured by the GERDA from the northwestern corner of the Great Bahama Bank near Bimini and the Great Isaac Light; two additional records were obtained along the western edge of the Little Bahama Bank. The depth distribution of this parthenopid crab on the insular side of the Straits appeared well delineated along the 100 fm isobath (183 m).

Ecological note. P. agona is mainly an inhabitant of both the inner and middle shelf hábitats of the Straits and whose vertical dispersion rarely extends outside the boundaries of the continental shelf. Undoubtedly, such a reduced depth range, coupled perhaps with the substrate requirements P. agona, are accountable for its apparent absence from the continental margin of the Straits at depths in excess of 200 m. This parthenopid has repeatedly been taken from sandy and broken-shell bottoms (Rathbun, 1925; Soto, 1972) very similar in composition to those occupied by P. agona on the insular side of the Straits.

Solenolambrus typicus Stimpson, 1871

Description. Rathbun, 1925, p. 537, text-fig. 148, pls. 192, 193, pl. 279, figs. 1-4.

Geographic range. Off North Carolina, Bahamas Bank, Straits of Florida, Gulf of Mexico, and Caribbean Sea.

Material examined. G-482, 2 m, 1 ovigerous f; G-925, 2 m; G-930, 1 m; G-1099, 4 f, 4 j; G-133, 1 m; G-110, 1 f, 1 j; G-722, 1 f; G-758, 1 m; G-757, 1 m; G-626, 1 ovigerous f; G-432, 1 m, 1 ovigerous f; G-238, 2 m, 5 j; G-239, 1 f; G-452, 1 m; G-462, 4 m, 1 ovigerous f; G-493, 1 ovigerous f; G-1327, 1 m; 1 ovigerous f.

Distributional analysis. S. typicus is a fairly common species in the area of the Straits; it ranked 8th among the ten most frequent deep-water brachyurans captured by the GERDA. The species was represented in the collection by a considerable number of individuals whose total relative abundance ranked 12th among the 86 brachyurans included in this report. (Tables 1 and 2). From 17 GERDA stations a total of 40 specimens were obtained, having a 1:1 ratio between males and females; six out of the 13 females were ovigerous. According to the value of the coefficient of dispersion of S. typicus (CD = 4.2) the spatial distribution of its individuals tends to follow a clustering pattern.

S. typicus occurred along the continental side of the southern and central sectors of the Straits and from the Pourtales Terrace crossed over to the insular side near Riding Rocks continuing northward into the Northwest Providence Channel and the western edge of the Little Bahama Bank. (Fig. 34).

The bathymetric range of this species extended from 183 m down to about 622 m; however, on the Florida side S. typicus seems to be a normal inhabitant of the outer shelf and the upper most part of the slope while on the insular margin the species is essentially concentrated about the 200 fm isobath (366 m).

Remarks. Earlier records ofS. typicus in the Straits have primarily been taken from the outer shelf off Fowey Rocks and the area adjacent to Key West. The species is also known to occur at the Little Bahama Bank (ALBATROSSstation 2655).

Ecological note. The type of distributional pattern of S. typicus in the Straits somewhat resembles that of its congeneric species S. tenellus; however, they seem to differ in their respective ecological requirements as far as depth and substrate are concerned. S. typicus showed affinity for poorly consolidated bottoms composed of mud ooze, sand, pteropod tests, and shell fragments. Likewise, its bathymetric range is wide enough to enable it to colonize parts of the Straits, namely the Pourtales Terrace where S. tenellus is conspicuously absent, in spite of the favorable habitat conditions that this area offers to a number of brachyurans. The thermal range of S. typicus allows this species to withstand temperature conditions above 14°C, curiously enough, there was not much temperature discrepancy between the insular and continental localities where this species occurred, regardless the depth difference noted before.

The likelihood of co-occurrence of the above two species in the slope environment of the Straits seems rather fortuitous. However, they may eventually share the same habitat on the continental shelf.

Solenolambrus tenellus Stimpson, 1871

Description.Rathbun, 1925, p. 541, pl. 194, figs. 3-4, pl. 279, figs. 5-9. Williams, 1965, p. 270, fig. 250.

Geographic range. Off Cape Lookout, N.C.: Straits of Florida; Bahamas; north coast of Cuba; Gulf of México, near Cape St. George, Fla.; Barbados.

Bathymetric range. 55 to 366 m.

Material examined. G-1328, 1 ovigerous f; G-1329, 6 m, 5 ovigerous f; G-982, 1 m; G-984, 1 m; G-924, 1 m; G-725, I ovigerous f; G-637, 1 f; G-983, 1 ovigerous f.

Distributional analysis. This small parthenopid, though not as frequent nor as abundant as its congeneric speciesS. typicus, appeared fairly frequently in the GERDA collection but always in reduced numbers. There were only two instances in which more than one specimen was collected from a single haul, and in those occasions as many as 11 were captured. A total of 18 individuals were identified having an equal ratio between males and females; nearly all the females were ovigerous stages. The examination of the distributional map ofS. tenellus in the Straits revealed two main centers of dispersion: the first one located at the northwestern end of Cay Sal Bank, and the second one at the northwestern corner of the Great Bahama Bank.

Fig. 34. Distributional pattern of Solenolambrus typicus collected by the GERDA

The bathymetric range of S. tenellus along the insular margin is clearly defined near the 100 fm contour (183 m), reaching its optimum depth at about 215 m.

Remarks. S. tenellus has been reported from the middle and outer shelf region of the area between Fowey Rocks and Key West (Rathbun, 1925).

Ecological note. In addition to the limited depth range exhibited by S. tenellus, the two main factors that seem to govern its dispersion in the Straits at depths in excess of 200 m are the nature of the substratum and the apparent restricted thermal tolerance of this parthenopid.

The substrate data available for this species clearly indicated the predominance of rough and rubbly bottoms primarily composed of coral debris, calcareous rocks,Halimeda remains, combined with mud and sand.

The temperature conditions prevailing at the depth level at whichS. tenellus occurred on the insular side roughly remain above the 18°C isotherm; apparently, the inability of this species towithstand temperatures bellow this isotherm may be responsible for its absence from the continental margin of the Florida side where waters warmer than 18°C are usually present on the continental shelf environment.

I am greatly indebted to Gilbert L. Voss for making available to me the GERDA collection of brachyurans obtained during the Deep-Sea Biology Program of the University of Miami. I wish also to thank J. C. Staiger, D. R. Moore, F. M. Bayer and L.P. Thomas for their critical review of the manuscript.

I greatly appreciate the valued assistance of L.B. Holthuis, during my stay at the Rijksmuseum van Natuurlijke Histoire in Leiden, The Netherlands. Thanks are also extended to D. Guinot and J. Forest, Muséum National d'Histoire Naturelle, Paris, for their help in solving some taxonomic problems. Thanks are due to R.J. Lincoln for allowing me to examine the Crustacea collection of the British Museum (Natural History).

I also wish to acknowledge the Intergovernmental Oceanographic Commission (UNESCO) for granting the funds which made possible the continuation of this study in Europe.

NOTE: While this paper was being reviewed, authors Manning and Holthuis described the new species G. fennari whose description is currently in press.

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