Ecteinascidia remanea, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 302-304

Ecteinascidia remanea n. sp.

( Fig. 79 )

TYPE MATERIAL. — Palau. Shrimp Lake, marine lake on E side Ngeruktabel Island, Ngeremdiu, mangrove roots/carbonate rock, 7°15.27’N, 134°26.68’E, 1 m, 26.XII.1994 ( MNHN P2 ECT 83).

ETYMOLOGY. — From the Latin remaneo: to remain.

DESCRIPTION

The specimens were attached to mangrove roots along with colonies of Eudistoma viride . The colony is a dense mass of zooids, stolons, and buds, compact enough to shelter Modiolidae molluscs, which usually are incorporated into the tunic of solitary ascidians. The stolons arise from the posterior three quarter, of the body length. They are ramified and fixed on the tunic of other adult zooids giving the colony the aspect of a tangled ball. The colour in life is not known. In formalin the zooids are transparent, and the blood sinuses and stolons are whitish.

The musculature consists of transverse fibres on each side of the cloacal siphon ( Fig. 79A, B ). The muscles are anastomosed and sometimes make a plexus. They extend more ventrally on the left side than on the right side of the body. There is no relation between the musculature of the oral siphon and the lateral musculature; these elements are separated by a large space. Even when contracted, the siphons are long; they possess eight lobes. We counted about 40 thin oral tentacles on a circle, in three or four orders of size, their bases joined. The prepharyngeal band has two high sides. The anterior one seems less developed but is distorted by numerous parasitic protozoans. The neural ganglion is round and protrudes into the branchial cavity. The neural gland channel begins at the posterior pole of the ganglion. It is wide and opens by a circular hole ahead of the prepharyngeal band. Anterior to the neural ganglion, the posterior side of the prepharyngeal band makes a large languet that is as long as the stigmata. This languet is linked to the rapheal papillae.

The branchial sac has 10 to 12 rows of stigmata. The first and last row are not complete and some stigmata extend over two rows. There are seven or eight rapheal languets (the two last ones are missing). A membrane half their height links them. There is some distance between the prepharyngeal band and the first row of stigmata. We counted 10 to 12 T-shaped papillae on each transverse vessel on each side of the body. We have not found junctions of these papillae to form longitudinal vessels.

The gut curves in a double loop. The anus and the top of the loop reach the same level ( Fig. 79A ) at the fifth or sixth transverse vessel. The globular stomach progressively narrows to form the intestine without constriction or poststomach. The typhlosole is the only groove to be seen on the internal side on the stomach. The rectum ends in an enlarged anus ( Fig. 79C ).

The ovary contains only a few eggs and can only be seen from the external side of the body ( Fig. 79A ). The testis is a mass of very small acini totally covering the ovary on the internal side ( Fig. 79C ). The sperm duct opens in the right cloacal cavity three stigmata rows posteriorly to the anus. This disposition merits the species name remanea . Only embryos at a morula stage were present in the cloacal cavity.

REMARKS

While the disposition of its musculature recalls that of Ecteinascidia styeloides (Traustedt, 1882) and Ecteinascidia nexa Sluiter, 1904 , the new species is characterised by three traits that are uncommon in the Perophoridae and until now have never been encountered together in the same species: a branchial sac devoid of longitudinal vessels having only T-shaped papillae, a stomach without a pyloric constriction, and a sperm duct opening posterior to the anus.

Family ASCIDIIDAE Herdman, 1882

Figures

FIG. 79. — Ecteinascidia remanea n. sp.; A, B, left and right sides of a zooid; C, internal side of the gut loop. Scale bars: 1 mm.