Eudistoma fluorescens, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 238-239

Eudistoma fluorescens n. sp.

( Figs 28 ; 116E )

TYPE MATERIAL. — Philippines. Bohol Sea, Balicasag Island SW of Bohol, 9°31.24’N, 123°41.11’E, 16.IV.1997 ( MNHN A3 EUD 179).

ETYMOLOGY. — Latinisation of fluorescent.

DESCRIPTION

The sand-free colonies form cushions 1.5 cm thick and 5 to 6 cm across. In life they are a bright orange spotted with irregular white patches, especially around the oral apertures ( Fig. 116E ). In formalin the colour turns uniformly brownish and the preservative itself takes on an iridescent colour similar to fluorescein (hence the species name). The zooids become slightly visible through the tunic when the colony is fixed. They constitute systems of rosettes, circular or oval. The rim of the oral siphon has a thin orange ring. The cloacal apertures are grouped in the centre of each system. The thoraces are perpendicular to the surface in the superficial layer of the colony, but the abdomens have no consistent orientation.

The zooids ( Fig. 28A ) measure up to 7 mm when relaxed. The oral siphon is short with six lobes: the cloacal siphon is a little longer, ending in six equal lobes or in four dorsal and two ventral lobes. The branchial sac is large, with more than 25 stigmata in a half row. The abdomen is considerably longer than the thorax, widened in the cardiac region and ending in several digitiform vascular appendages ( Fig. 28A ). The two muscular bundles coming from the thorax extend in two ribbons on each side of the abdomen and end by forming two horns at the bottom of the abdomen. The stomach is asymmetric. The gonads have numerous testis follicles in the gut loop posteri- or to the stomach.

There are up to five larvae incubated in the cloacal cavity. The most aged measure 1 mm for the trunk. They have three long adhesive papillae on a line alternating with four odd vesicles ( Fig. 28B ). A thickened crescent bulges on each side of the anterior trunk.

REMARKS

This species differs from all described Eudistoma species in its colour and the peculiar structure of the larvae.

Figures

FIG. 28. — Eudistoma fluorescens n. sp.; A, zooid; B, larva. Scale bars: A, 1 mm; B, 0.5 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.