A NEW RECORD OF Trichoplax adhaerens F. E. SCHULZE (PHYLUM PLACOZOA) IN THE MEXICAN CARIBBEAN SEA SCIENTIFIC NOTE

Trabajo recibido el 19 de septiembre de 1988 y aceptado para su publicación el 7 de octubre de 1988.

RESUMEN

INTRODUCCIÓN

More than hundred years ago, the german zoologist F.E. Schulze (1883) discovered a multicelular organism wich he namedTrichoplax adhaerens.As the name indicates, it looked like a plate (diameter: 1-3 mm), covered with "hairs" (flagella) on the upper and underside. With the latter it adhered to the substrate, in this case: the walls of sea water aquaria. The water of the aquarian originated from the Gulf of Trieste (Mediterranean).

A careful investigation led Schulze (1891) to the conclusion thatT. adhaerens had a very primitive organization. It had no organs, no polarity and no bilateral symmetry. Dorsoventrality was its dominant feature. Its structure included a dorsal and a ventral epitheflum separated by an interspace which consists mostly of water fluid, but contains also the so called fiber cells. The latter form a kind of connective tissue or "mesenchyme". Although the organism could move about and change its shape, no muscular and nervous system was discernible. Schulze did not hesitate, therefore, to regard T. adhaerens as the most primitive metazoon of all.

In spite of this significant findings, Schulze's discovery fell into oblivion. One of the reasons was that another zoologist,T. Krumbach (1907), expressed the suspicion based on rather poor arguments, thatT. adhaerens.was nothing else but the modified larva of a hydromedusa (Eleutheria krohnii).

The first author of this article had the opportunity of obtain in 1969 a sample of living microfauna from the littoral zone of the Red Sea (Eliat, Israel) in whichT. adhaerenswas abundant. After some experiments it became possible to takeT. adhaerens into cultivation. It turned out that the most suitable food organism was a marine species ofCryptomonas, a phototrophic fiagellate which has the advantage that it often rests at the bottom of a Petri dish.

As described by Schulze (1891),T. adhaerens can multiply by binary division, a phenomenon which in itself speaks against Krumbach's assumption. All further observations confirmed Schulze's opinion that T. Adhaerensin an "organism of its own" and the surviving representative of a Unique phylum, for which the namePlacozoa has been introduced (Grell, 1971). Most convincing was the observation that under certain conditions T. Adhaerens is capable of performing sexual reproduction and ambryonic development. However our knowlege about these processes is still fragmentary.

T. adhaerensoccurs in the Mexican Caribbean Sea. During a stay in April of 1988 at the Marine Station "Puerto Morelos" of the Instituto de Ciencias del Mar y Limnología, Universidad Nacional Autónoma de México, in Puerto Morelos, Quintana Roo, México, we found the animal in a small underground seawater deposit not far from the upper tidal level. This place is close to the landing-stage of the Marine Station.

A sample withT adhaerens was brought in a cooling box to the laboratory in Tubingen, where a pure culture was attempted. It was surprising that culturing was not possible with Cryptomonas, but only withChlorella (Protococcales) as food organism. It seems possible, therefore, that the individuals of Trichoplax from the Caribbean represent another ecological race of the only species know until today.

During the last twenty years the biology, histology and ultrastructure of T. adhaerens has been studied extensively, mots1y in the laboratories of K.G. Grell in Tubingen and A. Ruthman in Bochum (Summaries: Grell, 1980, 1981; Grell and Ruthmann, in press).

With respect to its geographical distribution,T. adhaerens is of widerspread occurence in tropical and subtropical seas. In addition to the Mediterranean and Red Sea and now in thw Mexican Caribbean Sea, there are reports from the littoral zone of Bermudas (Grell and Benwitz, 1981), Western Samoa (Marschall, pers. comm.), Japan (Sudzuki, 1977), Hawaii (Buchsbaum Pearse, in press) and from the Great Barrier Reef (Grell, cited, Buchsbaum-Pearse, in press).

We would like to thank the staff of the Marine Station "Puerto Morelos". E. Lozano, Alvarez, P. Briones Four zán and F. Escobar de la Llata, for help provided during the preparation of this note.

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