Eudistoma fucatum, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 239-240

Eudistoma fucatum n. sp.

( Figs 29 ; 116F )

TYPE MATERIAL. — Palau. Koror, SW end of Uchelbeluu Reef, wall, 7°16.54’N, 134°31.58’E, 7 m, 25.IX.97 ( MNHN A3 EUD 230).

ETYMOLOGY. — From the Latin fucatus: make up.

DESCRIPTION

The colonies are firm oval cushions with a sand-free surface. They are fixed by a part of their base, which is encrusted with some sand; there is no sand in the internal tunic. The colour in life was green ( Fig. 116F ) and turned brown in formalin. The zooids are arranged in circular systems that are very close to each other, with the cloacal apertures tightly grouped in the centre of each system. The tunic is very resistant in the upper layer of the colonies, more gelatinous inside when zooids are strongly retracted. The zooids ( Fig. 29A, B ) are perpendicular to the colony surface, but the abdomens often cross each other. When relaxed the zooids are 7 to 8 mm long, but only 3-4 mm when contracted. The cloacal siphon is longer than the oral siphon. Both siphons are black in formalin ( Fig. 29A ), and in some zooids the pigment extends onto the upper part of the thorax (hence the species name: fucatus means make-up). The remainder of the body is colourless and lies in a vitreous tunic.

The thoracic musculature is dense.

The dorsal part of the first row of stigmata is curved. The second row has 25 stigmata on each side. There is an unperforated area anterior to the branchial sac but not in the posterior part.

The abdomen is at least six times longer than the thorax ( Fig. 29A, B ). The stomach is posterior and short ( Fig. 29C ). The gut loop is straight. There are 30 to 40 round testis follicles in the gut loop. The ovary was not developed and no larvae were found. REMARKS

This species is mostly characterised by the very constant pigmentation of the tip of the siphons. The green colour of the colony in life and the arrangement of the zooids are also distinctive. The systems are so tightly packed together that the distance between the oral and cloacal openings of a zooid is greater than the distance between the oral openings of adjacent zooids belonging to different systems.

Figures

FIG. 29. — Eudistoma fucatum n. sp.; A, B two parts of a zooid; C, base of the abdomen. Scale bar: 1 mm.

FIG. 116. — A, Clavelina robusta Kott, 1990; B, Citorclinum laboutei Monniot F. & Millar, 1988; C, Cystodytes hapu Monniot C. & Monniot F., 1987; D, Eudistoma album Monniot F., 1988; E, Eudistoma fluorescens n. sp.; F, Eudistoma fucatum n. sp.