Molguloides cyclocarpa Monniot and Monniot, 1982

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 : 354-356

Molguloides cyclocarpa Monniot and Monniot, 1982

(®gure 31)

Molguloides cyclocarpa Monniot and Monniot, 1982: 127 ; 1985b: 33.

Molguloides sp. Monniot and Monniot, 1976: 652.

Material examined. St. 914, 5650±6070 m, one specimen.

Description. The specimen is nearly spherical, 39 mm in diameter. The thin transparent test is covered by short, sparse, unbranched hair-like outgrowths which become crowded around the apertures and a few become slightly longer ventrally. The apertures are widely separated from each other and do not project above the test surface, but the muscular body wall does have a long, tubular atrial siphon inside the test.

The body wall is thin but muscular. Eight or nine muscles radiate from the branchial siphon and two wide muscle bands extend from the lateral corners of the atrial siphon to the gonads. Relatively strong circular musculature, consisting of thin but numerous muscles, is present around the atrial siphon, but few circular muscles are around the branchial siphon. The whole body is covered by an irregular network of thin anastomosing muscles, most of them transverse and thicker and more numerous on the anterior two-thirds of the body. There are 13 branchial tentacles of three orders, with long and closely set branches of the ®rst order, and numerous short branches of the second and third orders. The prepharyngeal band consists of two low lamellae and makes deep undulations characteristic of the genus. The small dorsal tubercle has a longitudinal slit and is just above the neural ganglion and gland. The high dorsal lamina has a smooth margin. The branchial sac has eight high folds on the left and seven on the right, up to 13 longitudinal vessels on each fold and there are no vessels between the folds. The stigmata form large but interrupted rectangular spirals of up to 13 coils. The spirals are ¯at, protruding only slightly in the centre. Generally there are six transverse rows of spirals. The anterior transverse row is rather irregular and some spirals here show a tendency to be duplicated and others are reduced to a few short, wide, oval stigmata. The gut forms the loop characteristic for the genus and the rectum is unusually long. The gonads are deeply curved, the right has a U-shaped ovary with the axis orientated longitudinally and some distance from the small renal sac; the left gonad is nearly circular and is in the gut loop. Male follicles are along the outer side of the ovary and overlap its proximal end. The male ducts are joined to one common duct running along the mesial surface of the ovary. Male openings are evenly distributed along the whole length of the ovary, eight on the right gonad and four on the left.

Remarks. Molguloides cyclocarpa is an abyssal south Atlantic species reported from the Argentine Basin, South Georgia and the Cape Basin, from 3138 to 5208 m. The present specimen was recorded from the same region and at greater depth. Externally it resembles the photograph of M. cyclocarpa reproduced by Monniot and Monniot (1982, Plate 5B) so closely that they appear to be the same specimen. It diOEers from the original description in having an irregular network of thin muscles on the body wall. Monniot and Monniot (1982: 127) described and ®gured only muscles radiating from the branchial siphon and two strong muscle bands from the atrial siphon, which, with the shape of the gonads, constitute the most characteristic features of the species. They clearly stated that`other atrial muscles are not visible’. Their specimens were only a little smaller than the present one, and the greater development of muscles in the present specimen cannot be explained by its large size. We believe that Monniot and Monniot (1982) overlooked transverse muscles, which may be too thin, especially in comparison with the thick radial muscles.

The diOEerences between M. cyclocarpa and Caesira bathybia Hartmeyer, 1912 are not as clear as Monniot and Monniot (1982) thought. The characteristic muscle bands on the atrial opening could have been easily overlooked by Hartmeyer (1912), and when circular gonads are in a bad condition they resemble compact round masses. Nevertheless, until the type specimen of C. bathyphila is re-examined, M. cyclocarpa should be treated as a valid species.

Another closely related species with circular gonads and similar musculature is M. vitrea (Sluiter, 1904) . Thin, transverse body muscles are present, but they do not form as a dense network as in M. translucidus or in the present specimen and its musculature is intermediate between that of M. cyclocarpa and M. translucidus Monniot and Monniot, 1991 . However, M. vitrea diOEers in having numerous separate male openings, that do not form a common duct (see Monniot and Monniot, 1989b, ®gure 6).

Monniot and Monniot (1991) used diOEerences in the structure of the anterior rows of stigmata of the branchial sac as a stable character separating diOEerent species of Molguloides . This feature, however, seems to be more variable than they thought and it is unreliable when used to distinguish the species from one another. For example, Sanamyan and Sanamyan (1999) reported spirals of type B (six rows) for M. glans Monniot, 1978 , while according to Monniot and Monniot (1991) it has type D (eight rows). Nevertheless, the diOEerence between types B and D (both in one species) is greater, than between type C (seven rows) reported for M. translucidus and type E (eight rows) reported for M. cyclocarpa .

In arrangement of body muscles the present specimen strongly resembles Molguloides translucidus . Other internal features are also similar, although in M. translucidus the gut loop and intestine seem to be a little shorter, the renal sac is in contact with the right gonad and male follicles are more numerous. These features do not appear to be signi®cant species diOEerences. The specimens of M. translucidus were recorded from relatively shallow waters 650±700 m, far from the locality of the present specimen, from New Caledonia. The diOEerences could result from intraspeci®c variation in populations of a wide-ranging species.

All these facts suggest that M. cyclocarpa and M. translucidus are closely related and may be conspeci®c. The present record supports this opinion, although certain conclusions cannot be made without additional material. At this stage we are inclined to assign our specimen tentatively to M. cyclocarpa , rather than to M. translucidus , or a new species.