Synoicum Phipps, 1774

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 228-229

Genus Synoicum Phipps, 1774

Synoicum castellatum Kott, 1992 ( Figs 21 ; 115A)

Synoicum castellatum Kott, 1992a: 483 , fig. 44, pl. 8c-e. Type locality: Queensland, Australia.

MATERIAL EXAMINED. — Papua New Guinea. Louisiade, Calvados Island, Brooker Channel, 11°03.09’S, 152°28.62’E, 7 m, 1. VI.1998 ( MNHN A1 SYN 68).

DESCRIPTION

The colonies form large, firm, sand-free cushions about 2.5 cm thick. The colour in life is pale grey (Fig. 115A) or peach. Irregular round systems are conspicuous, well-separated at the colony surface. Each one forms a hollow in the centre of which opens the system’s common cloacal aperture as a round hole (Fig. 115A); at the periphery of the hollow there are about 30 closely placed oral siphons. In sections of colonies made in life the zooids are brown.

The zooids are large, some of them exceeding 2 cm in length. They lie perpendicular to the colony surface in a tunic that becomes brown in formalin. The oral siphon has six lobes ( Fig. 21A, C ), of which the ventral ones are often longer than the dorsal ones. The cloacal siphon forms a short tube with generally eight papillae on its rim. A simple languet ( Fig. 21A, C ), or sometimes a three-toothed one, is inserted a short distance from the cloacal opening but not on its rim.

The branchial sac contains 18 rows of elongated stigmata. Posteriorly the rapheal languets are displaced to the left side.

The abdomen is as long as the thorax in relaxed zooids ( Fig. 21A ), the oesophagus being particularly long. The stomach is cylindrical. Its wall is smooth in the most relaxed zooids, but with contraction a few longitudinal ridges appear ( Fig. 21C ), that in section turns out not to be true folds. There is a prominent annular post-stomach ( Fig. 21C ). The bilobed anus opens at the level of the thirteenth stigmata row.

The post-abdomen is especially long ( Fig. 21B ), with a very posterior ovary followed by the testis follicles. The gonads were poorly developed in our material, and no larvae were present.

REMARKS

Except for the cloacal languet, which is not on the rim of the cloacal siphon here, all characters correspond well to Kott’s description.

The present record in Papua New Guinea extends to the north the distribution of the species, which was known until now from western, northern and eastern Australia.

Family CLAVELINIDAE Forbes & Hanley, 1848

Figures

FIG. 21. — Synoicum castellatum Kott, 1992; A, B, two parts of a zooid; C, thorax and abdomen. Scale bar: A, B, 2 mm; C, 1 mm.