Corynascidia mironovi, Sanamyan & Sanamyan, 2002

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 : 333-335

Corynascidia mironovi sp. n.

(®gure 18)

Material examined. St. 4104, 5110±5120 m, 14 specimens. HOLOTYPE KIE 1/1031.

Description. The body is soft, test is thin and transparent, and preserved specimens are shapeless, about 2 cm in maximum dimension (®gure 18A). Few thick and short, root-like test outgrowths with thin terminal branches are present on the ventral part of the body. The opaque body is no longer attached to the test. The apertures are on short wide siphons and well removed from each other at opposite ends of the upper surface. The branchial siphon may have seven lobes, although these are shallow and irregular. Its dorsal side is higher than the ventral, thus directing the opening ventrally. The atrial siphon is plain-edged.

It is di cult to see the body muscles, even on stained specimens. The circular siphonal muscles are poorly developed and present only on a narrow area around the margin of each siphon. Those on the branchial siphon do not extend beyond the line of tentacles. Thick, short and more or less equally spaced transverse muscles cross the mid-dorsal line between the siphons. Similar thick muscles gather together on the dorsal side of the branchial aperture, their free edges orientated longitudinally and extending a little beyond the anterior margin of the branchial sac (®gure 18B, E). Two bunches of transverse muscles are present on dorsal and ventral sides of the atrial siphon, the ventral bunch crosses the rectum. Muscles were not detected on the ventral half of the body.

About 70 long, thin tentacles of several sizes arise from a low velum and project from the branchial aperture. The prepharyngeal band is some distance from the tentacles and is close to the branchial sac. It makes a distinct dorsal V around the small, simple dorsal tubercle. The elongate ganglion is just posterior to the tip of the dorsal V. The dorsal lamina has long languets with wide bases. The large cylindrical branchial sac has more than 30 transverse rows of spiral stigmata, separated by transverse vessels. The rows may be subdivided in two by transverse vessels. The branchial tissue is greatly reduced, the stigmata form rectangular meshes and resemble a spider’ s web (®gure 18D). Each mesh is crossed by two radial vessels. The limits of the meshes are di cult to determine and it is not possible to count exactly the number of the meshes per row, but apparently it is about 20 ±30. The branchial papillae arising from the transverse vessels are long and narrow, their length is approximately equal to the width of one row of stigmata. Most papillae are T-shaped, but rarely, terminal branches of two papillae from adjacent rows are connected to each other indicating their origin as longitudinal vessels. There are about two papillae per mesh.

The gut forms a short, narrow, straight loop on the right side of the posterior end of the body. The stomach, clearly demarcated from the intestine and oesophagus, is smooth externally, but has obscure and irregular internal folds. The rectum bends vertically and opens close to the atrial ori®ce. The anal border is smooth. Numerous small and oval male follicles are in the gut loop, and between the gut loop and the body wall. The thick sperm duct follows the rectum and opens near the anus. An ovary was not seen.

Remarks. The present species resembles C. translucida ( Monniot, 1969) in general body form, shape, position and size of the gut loop, and some other features (see Monniot, 1969, 1970). Corynascidia mironovi has diOEerent body muscles: in C. translucida they are present on the whole right side of the body and are absent on the left side. The two species have diOEerent stigmata and the branchial papillae are much longer in the present species. Another related species, C. alata Monniot and Monniot, 1991 , has poorly developed muscles, short papilla-like tentacles and a large lobed structure near the anus.

Corynascidia translucida was initially described under the generic name Agnesiopsis . The genus Agnesiopsis was characterized by position of the gut loop, clearly on the right side of the body, presence of spiral stigmata and T-shaped papillae, which are more numerous than the branchial meshes. The single diOEerence between these genera is the degree of development of the longitudinal vessels, which may be incomplete in some species of Corynascidia , and represented by few fragments in Agnesiopsis . Monniot and Monniot (1991) synonymized Agnesiopsis with Corynascidia and we agree with this opinion.

Etymology. The species is named after Dr A. N. Mironov from the Institute of Oceanology.