Ascidia sp.

Sanamyan, K. E. & Sanamyan, N. P., 2002, Deep-water ascidians from the south-western Atlantic (RV Dmitry Mendeleev, cruise 43 and Academic Kurchatov, cruise 11), Journal of Natural History 36 (3), pp. 305-359 : 337

Ascidia sp.

Material examined. St. 4100, 1265± 1376 m, one specimen.

Description. The specimen was attached to the test of Corella eumyota by the whole ventral side. It is small, the body removed from the tunic is 6 mm long. The branchial siphon is terminal, the atrial is in the posterior third of the body length and directed downward. The muscles are only on the right side where they form an irregular mesh. About 20 tentacles of three size orders arise from the margin of the low velum. A small, oval, dorsal tubercle has a simple round opening. The neural ganglion is close to the dorsal tubercle. The branchial sac has about 30 internal longitudinal vessels and lacks intermediate papillae. The visceral mass is in the posterior half of the body. The small globular stomach has several shallow longitudinal furrows, the intestine makes a vertical closed loop and the rectum is directed nearly horizontally. Gonads and excretory vesicles were not found.

Remarks. Only few species of the genus Ascidia are known from deep waters and only three species are distributed in Antarctic and Subantarctic waters: A. challengeri Herdman, 1882 , A. meridionalis Herdman, 1880 and A. translucida Herdman, 1880 . The present specimen diOEers from these species in several characters (shape of the gut loop, tentacles, dorsal tubercle), and although the diOEerences may be related to the size, we do not think the specimen belongs to any one of them. It seems to be closer to A. meridionalis , which has a small, simple, dorsal tubercle and lacks rib-like extensions from the base of the tentacles (as in A. challengeri ). The short, transversely directed rectum of the present specimen distinguishes it from A. meridionalis . In the shape of the gut loop, structure of the branchial sac and position of the ganglion close to the dorsal tubercle it resembles the north Atlantic A. tritonis Herdman, 1883 , but because of the unknown structure of the gonads, it is not possible to con®dently assign this juvenile specimen to a known species.