NEW RECORDS OF TWO SPECIES OF HYDROMEDUSAE (CNIDARIA) FROM THE MEXICAN CARIBBEAN

Trabajo recibido el 26 de agosto de 1991 y aceptado para su publicación el 18 de octubre de 1991

RESUMEN

INTRODUCCIÓN

Whilst studiying plankton collections, obtained during a survey program of the marine resources from the Yucatan shelf and Mexican Caribbean waters, new records for the area of hydromedusae species were encountered. Lizzia alvarinoae is the first Lizzia reported in the Atlantic Ocean and Thamnostoma tetrella has only been observed by Haeckel (1879) in Brazilian waters.

The examined material was collected by the O/V "Justo Sierra" of the Universidad Nacional Autónoma de México, during the PROIBE H (July, 1984), PROIBE IH (April, 1985), PROIBE IV (October, 1985) and PROIBE V (January, 1986) cruises, The surveyed area covered the Yucatan shelf obliquely using a Bongo net with 60 cm opening and mesh of 0.50 mm. Trawls were taken from different depths to the surface in the epipelagic region (0-200 m). Only the medusae obtained from one side of the Bongo net were analyzed. Zooplankton samples were preserved in 2% formaldehyde solution in sea water. The drawings were made freehand from preserved material.

Family Bougainvillidae

Lizzia alvarinoae Segura, 1980. (Fig.1)

Lizzia alvarinoae Segura, 1980: 515.

Previous records. Off Gulf of Tehuantepec, Mexico; off Peru coast; southwest Galapagos Islands (Segura, 1984).

Material examined

1 specimen collected 9/07/84 at station 12 (21° 21'N-86°33'W).

3 specimens collected 20/04/85 at station 57 (21°36'N-85°45'W); 1.

Specimen collected 21/04/85 at station 64 (21°05'N-86°30'W); 1.

Specimen collected 21/04/85 at station 69 (20°54'N-86°4TW); 1.

Specimens collected 22/04/85 at station 75 (20°07'N-86°59'W); 2.

Specimen collected 23104/85 at station 77 (19°51'N-87°16'W); 1.

Specimen collected 13/10/85 at station 102 (21°25'N-86°15'W); 1.

Specimens collected 26/01/86 at station 130 (21°02'N-86°43'W); 3.

Specimens collected 26/01/86 at station 135 (20°46'N-86°28'W); 3.

Specimen collected 27/01/86 at station 145 (19°50;N-87°23'W); 1.

Specimen collected 28/01/86 at station 146 (10°40'N-87°17'W).

Remarks. The genus Lizzia was stablished in 1,846 by Forbes. Seven species are currently recognized, and L. alvarinoae is the only species presently known to occur on both sides of the Isthmus of Panama. The presence of this species in the Mexican Caribbean and in scattered eastern tropical Pacific localities, can be explained as a remnant species from the Tetchy Sea fauna (Fig. 1).

Lizzia alvarinoae was originally described from the eastern tropical Pacific by Segura (1980). The collection of L. alvarinoae in the Mexican Caribeean represents the first Caribbean and Atlantic record for the species.

Thamnostoma tetrella Haeckel 1879). (Fig. 2)

Thamnites tetrella Haeckel 1879: 84; Mayer, 1910: 152; Vannucci, 1951: 106.

Thamnostoma tetrella Rees, 1938: 25; Kramp, 1959:106.

Figure 1. Lizzia alvarinoae collected from the Mexican Caribbean, showing the medusa buds on the stomach.

Figure 2. Thamnostoma tetrella collected from the Mexican Caribbean, showing the oral tentacles divided twice.

Previous records. Brazilian coasts (Haeckel, 1879).

Material examined. 1 specimen collected 5/10/85 at station 8 (22°10'N-89°04'W); 2 specimens collected 7/10/85 at station 23 (22°44'N-88°02'W); 2 specimens collected 15/01/86 at station 13 (22°53'N-88°30'W) (Fig. 2).

Remarks. The genus Thamnostoma includes five species, one of them have been found more than a few times, and they are distinguished from each other by relative characters (Table 1). The Caribbean specimens differ little from the original description. The Caribbean specimens are smaller in body lengths and the oral tentacles are divided two times only.

Thamnostoma tetrella has not been observed out of Brazil since the species was first described by Heackel (1879) in this region. The collection of Th. tetrella in the Mexican Caribbean waters, represents an extension into the northern range of this species (Table 1).

TABLE 1 DIFFERENTIAL CHARACTERISTICS OF SPECIES OF THAMNOSTOMA.

The author wish to thanks to Patricia Briones F. for loaning the plankton collections of the PROIBE cruises.

Thanks are also due to Brigitt van Tussenbroeck and José Alvarez Cadena for his comments on the manuscript.

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