Polysyncraton vestiens, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 275-276

Polysyncraton vestiens n. sp.

( Figs 58B ; 59 )

TYPE MATERIAL. — Palau. Koror, Lighthouse Reef Basin, 7°17.90’N, 134°28.34’E, 47 m, 20.VII.1998 ( MNHN A2 POL 95).

ETYMOLOGY. — From the Latin vestiens : clothing.

DESCRIPTION

The thin colonies are encrusting, 1 mm thick. They are very soft, semitransparent, and colourless in formalin preservative. The resistant tunic is only present in a superficial and basal layer and around the zooids, which are isolated in small groups in bridges uniting the surface to the base of the colony. The spicules are not dense and allow one to see the zooids through the tunic. There is no special accumulation of spicules around the oral siphons. The six oral lobes are low around the rim of a narrow siphon. The cloacal aperture uncovers most of the branchial sac ( Fig. 59A ). The dorsal languet is very variable, sometimes short and round but sometimes very large and T-shaped ( Fig. 59A ). The lateral thoracic organs, extremely small (or absent), lie at the level of the second transverse sinus or the second stigmata row. There is no retractor muscle. There are 10 to 12 stigmata in the first half row. The oesophageal peduncle is long and the abdomen, smaller than the thorax ( Fig. 59A ), is folded under the thorax. The abdomen has the usual components of the genus. The gonads lie in the gut loop. The testis is made of three to six lobes in a protruding rosette ( Fig. 59A ). The well-developed sperm duct is coiled in three turns above the centre of the testis rosette. The ovary matures after the testis.

Numerous larvae are present in the basal layer of the colony after the gonads have regressed. The trunk is 0.7 mm in length, the tail makes three quarter of a turn around it. There are three wellseparated adhesive papillae on long stems and eight pairs of finger-like ampullae, resulting from the division of the four original pairs ( Fig. 59B ). There is one bud on each side of the larval visceral mass ( Fig. 59B ).

The very small spicules ( Fig. 58B ) are stellate, with numerous short rays: their diameter is 30 µm.

REMARKS

This species is closely allied to Polysycraton purou Monniot C. & Monniot F., 1987 from Polynesia and closely resembles it in its appearance and the structure of the larvae. It differs from P. purou in smaller spicules that are also present around the zooids, a wider cloacal aperture, and the absence of a retractor muscle.

Figures

FIG. 58. — Spicules; A, Polysyncraton cerebellum n. sp.; B, Polysyncraton vestiens n. sp. Scale bars: 10 µm.

FIG. 59. — Polysyncraton vestiens n. sp.; A, zooid; B, larva. Scale bars: 0.5 mm.