A New Species of Pla Tidia (brachiopoda) from the La Chapelle Bank Region

A new species of Platidia (Brachiopoda, Platidiidae) was dredged by R.V. 'Sarsia' in November 1956 in the La Chapelle Bank region, attached to the dead part of the coral Anisopsammia rostrata (Pourta1es).1 Eight entire specimens and two smashed were dredged at position 47° 30' N., 7° 20' W. at a depth of 870 to 970 fathoms, and one at position 47° 38' N., 7° 28' W. at 710 to 750 fathoms. All, except the two smallest, were a reddish brown, the coloration being due to a deposit of manganese oxide: the natural colour is a yellowish white. The dead coral was almost black with the same deposit (see Southward, 1958, p. 644). Some individuals were transversely oval, others somewhat rectangular and irregular in shape, according to the surface of attachment (Fig. I). The Anisopsammia was fairly free of encrusting organisms but the polyps are closely spaced and therefore apt to interfere with the regular spreading of the closely attached Platidia. The new species of Platidia was difficult to deal with. As it was from deep water it was brought back in a refrigerator at a temperature of 5°-7° C: specimens then went into laboratory tank water of 13° C. It has been found that brachiopods generally cannot withstand sudden changes of temperature, and it was this change in temperature which no doubt adversely affected the specimens, most of which showed separation of the cells of the epithelium of the filaments after a few days. Those opened the day after arrival in the laboratory did not extend the filaments on the anterior region of the lateral arms, although the posterior and lateral filaments and those on the posterior extremities of the lateral arms expanded well. This continued contraction of the filaments of the anterior region of the arms may be dependent in some way on the fact that the arms remained depressed and did not raise themselves as they do under similar conditions in P. davidsoni and P. anomioides. Attempts were made to narcotize the animals with I % stovaine and with 7 % magnesium chloride, a drop added at intervals to a small dish or watch glass of sea water. The latter acted rather the better, but results were not good. The specimen with most expanded lophophore is shown in Fig. 5: it is not