Adagnesia charcoti Monniot and Monniot, 1973

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 : 328-330

Adagnesia charcoti Monniot and Monniot, 1973

(®gures 15B, 16A) Adagnesia charcoti Monniot and Monniot, 1973: 424 ; 1976: 634; 1985a: 284; Monniot, 1994; Sanamyan and Sanamyan, 1999: 1844 (synonymy).

Material examined. St. 4104, 5110±5120 m, two specimens.

Description. The dorso-ventrally ¯attened, disk-shaped body is 13 mm in greatest diameter. The test is naked and transparent, it is thick on the upper (dorsal) half of the disk and thin on the ventral half. Few hair-like processes are present only around the margin of the body. The branchial aperture has six triangular lobes, the atrial has seven.

A few thick circular muscles are present around the branchial aperture, and numerous thinner muscles around the atrial opening. About 20 thick longitudinal muscles radiate from each siphon. On the left side, muscles radiating from the atrial siphon are interrupted. A wide band of ®ne parallel transverse muscles crosses the mid-dorsal line posterior to the atrial siphon across the rectum.

Numerous long branchial tentacles arise from the outside of a high velum. The prepharyngeal band makes a dorsal V; and papillae were not detected in the prepharyngeal area. Long dorsal languets arise from the wide imperforate middorsal portion of the branchial sac. The branchial sac has ten rows of about the same number of square spiral stigmata, each with up to 2.5 coils. The rows are separated by transverse vessels with T-shaped papillae, about two papillae per spiral.

The gut forms a small closed loop, the stomach is small and its limits are not clear. Gonads are well developed, the ovary and testis follicles being in the gut loop and spread over it. Thick gonoducts run along the rectum and open anterior to the lobed anus.

Remarks. Most characters of the present specimens are in good agreement with previous descriptions and we have no doubt in the present identi®cation. As in the specimen from Macquarie Island (see Sanamyan and Sanamyan, 1999), we failed to ®nd any papillae in the prebranchial area of the present specimens. Such papillae were mentioned and ®gured in the original description of A. charcoti , as well as in other descriptions provided with ®gures ( Monniot and Monniot, 1985a; Monniot, 1994), excepting a specimen from the Argentine Basin (Monniot and Monniot, 1976). The latter specimen was listed (Monniot and Monniot, 1976, table 1) as Adagnesia sp. , but was then described as A. charcoti . It closely resembles our specimens, although it has thinner and less regular muscles.

This is the ®rst record of the species below the Antarctic Convergence. The species previously was known from numerous records from the Atlantic and also was recorded from the Indian Ocean (Amsterdam Island) and Macquarie Island.