Distaplia regina Kott, 1990

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 257-259

Distaplia regina Kott, 1990

( Fig. 45 )

Distaplia regina Kott, 1990: 125 , fig. 44c. Type locality: Australia, Queensland. — Monniot F. & Monniot C. 1996: 216, fig. 38B, C, pl. 7A, Palau.

MATERIAL EXAMINED. — Palau. Koror, West Malakal Harbour mouth, 7°20.37’N, 134°25.78’E, 40 m, 21. V.1994 ( MNHN A3 DIS 76).

DESCRIPTION

The colonies are club-shaped, or cushion-like sometimes with a short peduncle. They reach 3 cm in height and 1 to 3 cm in diameter. The colour in life is slightly translucent cream, and the consistency is firm and rubbery. No sediment is embedded. The zooids are arranged in lines converging at the apex of the colony, where the common cloacal cavities open.

The zooids are in the outer part of systems, while the large larvae are incubated near the centres of the systems. The wide thorax has a large cloacal opening ( Fig. 45A ). The languet is either triangular or enlarged with its rim cleft into several teeth when it is close to the common cloacal aperture. The thoracic muscles are mostly longitudinal, thin but dense. There are 12 oral tentacles of two sizes.

The branchial sac has more than 20 stigmata even in the posterior half row. They are not crossed by parastigmatic vessels. Numerous stigmata are already pierced in buds. The gut loop is twisted. The round stomach has an areolated wall ( Fig. 45B ). The intestine lacks definite compartments; its shape depends on the gut contents. The anus has two large lobes.

Clear vesicles occur along the whole length of the gut. Ten to 15 testis follicles in a cluster occupy the centre of the gut loop, with the ovary against them ( Fig. 45B ). The sperm duct is straight.

The vascular process is thin and short. The larvae are very large, 2 mm for the trunk ( Fig. 45C, D ). They are isolated early from the mother zooid into a pedunculate brood pouch. The tail does not reach around half the trunk. The three adhesive papillae, in a triangle, are circled at their base by large irregularly shaped ampullae whose number is not constant ( Fig. 45C, D ). The larval gut and branchial sac are developed early, and the clear pyloric vesicle already is apparent.

REMARKS

This species has been collected at the same station as Distaplia mikropnoa , which differs in having a plicated stomach wall, gonads in a long pedunculate pouch posterior to the abdomen as in Distaplia stylifera , and much smaller larvae Larger but not brooding specimens were previously collected in Palau (Monniot F. & Monniot C. 1996).

The species is presently known from Australia and Palau.

Distaplia stylifera ( Kowalevsky, 1874) (Fig. 119C)

Didemnum stylifera Kowalevsky, 1874: 43 . Type locality: Red Sea.

Distaplia stylifera – Millar 1975: 224. Synonymy: see Monniot C. & Monniot F. 1984: 571. — Monniot F. 1988: 197, fig. 1. — Kott 1990: 127, part.

MATERIAL EXAMINED. — Philippines. Bohol Sea, Balicasag Island SW of Bohol, 9°31.24’N, 123°41.11’E, 12 m, 16.IV.1997 ( MNHN A3 DIS 75).

DESCRIPTION

In the Philippines, this species occurs as pale yellow cushions about 1 cm thick. The oral siphons are arranged in circles around round common cloacal apertures (Fig. 119C). The colony surface is either flat or has grooves delimiting the systems. The zooids are perpendicular to the colony surface. Young zooids have a tubular cloacal siphon, but in aged zooids the cloacal aperture is large with a large upper languet and a shorter or absent posterior lip. The oral siphon has six short lobes. The thorax has numerous longitudinal muscular fibres. The four rows of stigmata are each cut by a parastigmatic vessel, which is not complete in the youngest zooids. There are on average 20 stigmata in a half row. The stomach is oval with thickenings forming longitudinal folds that are irregular and often cut. There was no obvious regional differentiation in the intestine. A large, spherical pyloric ampulla lies in the gut loop.

Both the male and female gonads are located in a pouch on a long peduncle below the abdomen. The testis follicles are not numerous, about five. The ovary lies against the testis. The sperm duct is straight.

The incubatory pouch, with a long peduncle, normally contains a single embryo. The larva has a well-pigmented ocellus and an irregular brown otolith. The three adhesive papillae are short and in a triangle. The larva has already four rows of stigmata. The tail describes half a circle around the trunk.

REMARKS

This material corresponds well to other specimens described from the Atlantic, Indian, and Pacific Oceans. It differs from other Distaplia species with pedunculate gonads:

– D. australensis Brewin, 1953 has pedunculate colonies, a single common cloacal aperture, and no parastigmatic vessel;

– D. knoxi Brewin, 1954 has a pedunculate colony and no parastigmatic vessels;

– D. mikropnoa ( Sluiter, 1909) has pedunculate colonies, no parastigmatic vessels, and systems of a different shape than D. stylifera ;

– D. prolifera Kott, 1990 has large zooids, circular systems, and parastigmatic vessels, but the stomach does not have folds;

– D. tokioka Kott, 1990 and D. violetta, Kott, 1990 are sessile: they have parastigmatic vessels and few stomach folds;

– D. skoogi Michaelsen, 1934 has a smooth stomach; – D. stylifera may have very different colony shapes at one locale: completely sessile and encrusting colonies or pedunculate ones. The systems are always circular. The species is widely distributed in tropical areas of all oceans.

Figures

FIG. 45. — Distaplia regina Kott, 1990; A, zooid; B, abdomen; C, D, larvae. Scale bar: 1 mm.