Seriocarpa tongae, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 319-320

Seriocarpa tongae n. sp.

( Figs 89 ; 127E)

TYPE MATERIAL. — Tonga. Vava’u, Fotula, small rock off West coast of Vava’u, cave, 18°38.92’S, 174°04.12’W, 33 m, 16.XI.1997 ( MNHN S1 SER 8). ETYMOLOGY. — Named after Tonga, the type locality.

DESCRIPTION

The individuals were grouped in patches, loosely attached to the substratum. Even when the bodies are close together, we have not found any anatomical link between them. The bodies are covered with hair-like extensions of the tunic and are coated with sand and diverse epibionts (Fig. 127E). Both siphons, far apart, are red.

When removed from the tunic, the body is elongated with the siphons widely spaced ( Fig. 89A ). There is a mid-ventral keel between two parallel grooves in the body, which are filled with tunic, and which contain the gonads ( Fig. 89B ). The body wall is thin. The musculature comprises crossed longitudinal and transverse fibres on the siphons, but there is only transverse musculature, made of thin but dense fibres, in the remainder of the body wall.

There are about 20 long oral tentacles in two orders of size, irregular, with some small buttons between them. The prepharyngeal band is indented dorsally in a deep V. The dorsal tubercle is round; its opening is a vertical or transverse slit.

The dorsal lamina is a long, high membrane with a plain edge.

The branchial sac has four high folds on each side, on which the vessels are pressed together. One of the formulae is:

R.E. 1 7 7 9 5 7 6 9 3 D.L. 2 9 7 8 6 9 6 9? E.L. There are no parastigmatic vessels.

The gut is small, and lies very posterior in a closed loop ( Fig. 89A ). The oesophagus is very short. The stomach is elongated with a dozen uninterrupted deep folds. No caecum was found. The anus has numerous small lobes.

The gonads are numerous, included in parallel rods of tunic penetrating into the body wall on each side of the endostyle ( Fig. 89B ). The polycarps are not in a line, but rather in two longitudinal series with up to 30 gonads on the right side and a few less on the left. Each polycarp is enclosed in a capsule of tunic, and only the genital ducts open into the cloacal cavity ( Fig. 89C, D ). Each gonad consists of a round ovary accompanied by a single male follicle. The sperm duct is inflated into an ampulla, then narrows before it opens close to the female papilla ( Fig. 89C, D ).

Numerous endocarps are scattered over the whole internal side of the body wall.

We have not found cloacal tentacles at the base of the cloacal siphon.

REMARKS

S. tongae n. sp. is the fifth species described in the genus.

Seriocarpa benthedi Monniot C. & Monniot F., 1985 is very different from all others. It is a very small deep sea species with few gonads and only three rows of stigmata.

Seriocarpa cristata Millar, 1975 from Kei Island is the most closely allied to our species, with a similar size, gut, and branchial sac, but its gonads are less numerous and lie in a single line on each side of the endostyle.

Seriocarpa littoralis Millar, 1975 from Singapore has many more oral tentacles, more longitudinal vessels on the branchial folds, a short stomach, and gonads that are differently included in the tunic.

Seriocarpa rhizoides Diehl, 1969 has a wide distribution in the Atlantic Ocean, the Mediterranean Sea and the Pacific Ocean. It has a single midventral rod of tunic penetrating into the body wall and containing a double row of gonads. The tunic has stout root-like extensions instead of fine hairs. Its colonial nature has been demonstrated.

Figures

FIG. 89. — Seriocarpa tongae n. sp.; A, specimen ventrally opened; B, external view of the ventral side; C, lateral view of a gonad; D, internal view of a gonad. Scale bars: A, B, 0.5 cm; C, D, 0.5 mm.