Eudistoma toealense Millar, 1975

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 245-246

Eudistoma toealense Millar, 1975

Eudistoma toealense Millar, 1975: 222 . Type locality: Toeal. — Monniot F. & Monniot C. 1996: 194, fig. 32, pl. 5E, Palau, Indonesia.

MATERIAL EXAMINED. — Palau. E Ngeruktabel, Big Fish Lake, marine lake, 7°15.81’N, 134°24.91’E, 0.5 m, 11.VII.1994 ( MNHN A3 EUD 133).

Federated States of Micronesia. Chuuk, E Dublon, mangrove lagoon, 7°22.90’N, 151°53.55’E, 0.5 m, 9.VII.1992 ( MNHN A3 EUD 134). — Yap, Tagreng, 9°33.38’N, 138°08.45’E, 0.5 m, 6.VIII.1995 ( MNHN A3 EUD 155). — Pohnpei, Saladak, 6°55.81’N, 158°16.90’E, 1 m, 13.X.1996 ( MNHN A3 EUD 168).

Eudistoma tumidum Kott, 1990 ( Figs 34 ; 117D)

Eudistoma tumidum Kott, 1990: 232 , fig. 91. Type locality: Australia, Gulf of Carpentaria.

MATERIAL EXAMINED. — Philippines. Mindanao, Davao, NE side of Samal Island, 7°09.63’N, 125°47.05’E, 10 m, 30.III.1996 ( MNHN A3 EUD 226).

DESCRIPTION

The colonies are thick, encrusting cushions, 2.5 cm thick and 5 cm across. The surface is smooth with irregular swellings depending on the substrate. The colour is a translucent light grey, with pale yellow spots (Fig. 117D) that correspond to visible zooids and faecal pellets. The zooids are arranged in circular systems. There is no embedded sediment but rather abundant faecal material.

The zooids ( Fig. 34A ) are slender when relaxed, 8 mm long, perpendicular to the colony surface. Both siphons have six lobes; the cloacal siphon is often a little longer than the oral. The thoracic musculature comprises numerous dense transverse fibres and about 15 evenly spaced longitudinal bundles, which extend in two ribbons along the abdomen. There are three rows of oral tentacles. The branchial sac has about 25 stigmata on each side in the first row, which is slightly curved anteriorly.

The abdomen is much longer than the thorax. The stomach lies only half or two third down the length of the abdomen ( Fig. 34A, B ), so there is more space as usual in the genus for the gonads. The gut loop is straight when the zooid is extended. The round testis lobes are numerous (≈ 40) throughout the space below the stomach ( Fig. 34B ). The ovary lies centrally among these male lobes. One to four larvae are incubated in the cloacal cavity. They are rather small, 0.65 mm for the trunk, and only one matures at a time ( Fig. 34C ). They have three adhesive papillae, which are not equidistant, and six ampullae on each side; the four central ones are branched, giving an appearance of two series of ampullae.

The ocellus and otolith are present. The larval branchial sac is not yet differentiated.

REMARKS

By its colony shape, the circular systems of zooids, and the structure of the larva, this species closely resembles E. ovatum ; but it does not contain sand and the larvae are much smaller, with fewer ampullae.

Figures

FIG. 34. — Eudistoma tumidum Kott, 1990; A, zooid; B, base of the abdomen; C, larva. Scale bars: A, B, 1 mm; C, 0.25 mm.