Eudistoma inauratum, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 241-242

Eudistoma inauratum n. sp.

( Figs 31 ; 117A)

TYPE MATERIAL. — Palau. Mecherchar, Jellyfish Lake, marine lake, on carbonate rock, 7°09.83’N, 134°22.50’E, 1 m, 8. VI.1994 ( MNHN A3 EUD 178).

ETYMOLOGY. — From the Latin inauratus: golden.

DESCRIPTION

The colonies are cushions several centimetres in diameter, constituted of several lobes whose short peduncles arise from a common base. The general colour in life is orange (Fig. 117A) with paler siphonal openings; the colony turns dark brown in formalin. The tunic’s consistency is firm and there is no impregnation of sediment. The zooids are not arranged in systems. Zooids are elongat- ed, up to 12 mm long ( Fig. 31A, B ).

Both siphons are short with six lobes. The branchial sac was too contracted to count the stigmata. The oesophagus is particularly long, reaching to a stomach that lies in the very rear of the abdomen ( Fig. 31B ). The stomach is elongated, separated by a narrowing from the mid-intestine. The rectum is wide from its origin at the bottom of the gut loop and runs straight to the anus in the thorax.

The gonads comprise an elongated group of numerous testis follicles in the bottom of the gut loop, and an ovary located at the centre of this array ( Fig. 31B ). A thin and long vascular process extends from the bottom of the abdomen.

The larvae are brooded in the oviduct ( Fig. 31A ) beside the oesophagus, behind the thorax. There may be four embryos at a time at different stages of development. They inflate the body wall but do not make a pouch.

The larvae ( Fig. 31C ) have a trunk 0.9 mm long. The curled tail is short and does not reach even the anterior pole of the larva. The three adhesive papillae on a line are not regularly spaced, the two dorsal ones being closer to each other than to the ventral one. They are separated by a variable number of elongated vesicles that are flattened dorso-ventrally. Their extremity is pointed and they bear small, very irregular ramifications.

The ocellus and otolith are clearly visible, but no differentiation of the larval organs is apparent.

REMARKS

The combination itself of several characters isolate this new species from all other Eudistoma : colonies with erect lobes on a common base, the orange colour, the absence of systems, the oesophageal brooding, and the larvae with irregularly spaced adhesive papillae.

Figures

FIG. 31. — Eudistoma inauratum n. sp.; A, B, two parts of a zooid; C, larva. Scale bars: A, B, 1 mm; C, 0.5 mm.