Corella brewinae Monniot, 2013, n. sp.

Corella brewinae n. sp.

Figs 4 B, 7, 8, 9.

Material examined

- Amsterdam Island SE, 11/01/ 1972, 80m, coll. Beurois. Syntypes (MNHN P4 COR.A 12) - New Zealand, Otago harbour, wharf, 2012, coll. A. Wood. - Stewart Island, 1875, coll. Filhol.

- 54°31’S –159°00 E, 110m, 18/06/1968, Eltanin survey USA.

The body shape varies but is more or less oval. The specimens up to 5cm in length are often found in aggregates of different sizes, and these clusters (Fig 4 B) are very similar to those of C. eumyota living in the same habitat. In life, the tunic is not completely smooth but wears irregular small papillae. The colour is pale yellow. Both siphons have 6 lobes. The oral aperture is apical and the atrial siphon opens at mid distance of the dorsal line. The body wall is thin and the musculature is visible through it (Fig. 7 A). Apart from the siphon sphincters, the muscles are essentially located over the left side with interlaced fibres grouped in ribbons (Fig 7 A). On the anterior part of the right side some longitudinal fibres are present but do not reach the level of the digestive tract. The oral tentacles are thin and long, we counted about 60 to 75 distributed in 3 orders of length in specimens 2.5cm long. The prepharyngeal band has two blades indented in a V dorsally and prolonged on the dorsal line in a groove (Fig. 8 D) as in C. eumyota and C. antarctica. The dorsal tubercle forms a C opened anteriorly with horns rolled inside (Fig 8 D).

About 52 dorsal languets of equal size were counted in several specimens. The branchial tissue is flat, linked to the body wall by wide tubular structures ramified irregularly, less dense than those present in C. antarctica. The longitudinal vessels, 37 to 40 on each side, are held on wide papillae (Fig. 8 A, 9B). The spiral stigmata are not regularly aligned as many secondary spirals are intercalated. Each spiral is interrupted several times. The number of turns is difficult to evaluate it varies from 3 to 4, rarely 5.This number is larger than in the branchial sac of C. eumyota and smaller than in C. antarctica.

The gut loop occupies a large part of the right body side (Fig. 7 B, 9A,C). The oesophagus is curved and narrow. The stomach is globular (Fig. 8 B) but hardly visible when the gonads are very developed. It has 8 to 9 internal longitudinal folds and externally a long typhlosolis between oblique folds. The intestinal loop is vertical, the intestine curves below the oesophagus in a straight rectum tightly linked to the body wall. The anus rim has numerous round lobes Fig. 8 C). The gonads (Figs 7 B, 8B, 9AB) are distributed above the gut loop. The ovary is mainly located inside the top of the loop and over the internal side of the stomach and intestine but a mass of mature eggs can be seen nested in the loop in several specimens (Fig. 7 B). The testis lobes are small covering the intestine on its interior and exterior sides. Parts of wide branches of the ramified sperm duct may appear on the external side of the intestine (Fig. 9 C). The common sperm duct passes between the oesophagus and the intestine, follows the rectum an opens in a short papilla against the anus rim (Fig. 8 C arrow). The oviduct follows the sperm duct and opens in a simple hole against the male papilla but it is difficult to see. The heart can be seen along the stomach and ascending limb of the intestine but is not prolonged anteriorly on the body wall.

C. brewinae is very similar in shape and size to C. eumyota. However it differs from it by the long gonad ducts but also by the dorsal tubercle and a larger number of spirals of the stigmata. It differs from C. antarctica by the dorsal rapheal languets the shape of the genital papillae and a lower number of turns of the spiral stigmata. Nevertheless the 3 species are closely related and share a similar musculature design.