Molgula millari Kott, 1971

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 : 352-353

Molgula millari Kott, 1971

(®gure 29)

Molgula millari Kott, 1971: 70 . Monniot and Monniot, 1982: 124.

Material examined. St. 4093, 3700±3970 m, one specimen.

Description. The oval specimen is about 13 Ö 10 mm. The body is entirely covered by short hair-like processes (less crowded ventrally) with attached sand grains. The apertures are beneath two separate transverse folds of the test, well separated from one other and at opposite ends of the upper surface of the body.

The shape of the internal siphons is peculiar: they are short, directed away from each other, and much ¯attened dorso-ventrally, so that it appears as if they consist of a larger dorsal lip and a smaller ventral one. The margins of the siphons are smooth, but a short distance from the margin, inside the siphon, are six long, pointed, tentacle-like outgrowths, corresponding to siphonal lobes of other Molgulidae . They are thin and thread-like in the atrial siphon, while in the branchial siphon the two dorsal ones are much larger than others. The body is entirely enclosed in a layer of thin, circular anastomosing muscle ®bres. About 12±18 thick, internal radial muscles arise from the lateral corners of each aperture and form two isolated muscular areas on each side of the body (®gure 29).

About 13 large and medium-sized tentacles, and numerous small crowded tentacles, are on the short muscular velum. The tentacles have branches of the ®rst, second and third orders. The prepharyngea l band is composed of a single, unusually high lamella which makes a deep dorsal V around a minute dorsal tubercle and neural ganglion and continues dorsally into a smooth-edged dorsal lamina. The prepharyngeal band is separated from the ring of tentacles and the perforated part of the pharynx, but longitudinal branchial vessels arise just behind it. The branchial sac has seven high folds consisting only of longitudinal vessels, while the wall of the branchial sac is nearly ¯at. Such a structured branchial sac is more characteristic for Molguloides . There are no longitudinal vessels between the folds. The branchial formula is: E(5)(6) (5) (7)(7)(7) (6)DL (5) (7)(5)(5) (5)(6)(5)E. The stigmata form ¯at interrupted spirals of ®ve to seven coils. Small interstitial spirals are present.

The gut forms a narrow, straight primary loop parallel to the endostyle, with the straight rectum bending at a right angle to it. The oesophagus is short and straight, the stomach completely hidden under large, scalloped liver pouches, the anal border is bilobed and smooth-edged. The left gonad is along the descending branch of the primary gut loop, the right is in close contact with the postero-dorsal side of the renal sac. Each gonad consists of a thick, tubular ovary and numerous elongate male follicles, scattered along the ventral side and proximal end. One male opening is on the right gonad and two on the left. They are on the ends of short ducts on the dorsal side of the gonad, some distance from the short terminal oviduct.

Remarks. This species was originally described from the south Indian Basin (type locality) and from Tasmania and Macquarie Island. The present specimen was recorded from nearly the same place, and the same depth as Monniot and Monniot’s (1982) four specimens assigned to this species, which are similar to the present one, including the presence of two male papillae on the left gonad. All three specimens described by Kott (1971) have a shorter rectum. It is possible that the Atlantic specimens are distinct from Kott’s species, but at present we are inclined to follow Monniot and Monniot (1982) and identify them as M. millari .