Molgula longitubis, Monniot, 2002

Monniot, Claude, 2002, Stolidobranch ascidians from the tropical western Indian Ocean, Zoological Journal of the Linnean Society 135 (1), pp. 65-120 : 116

MOLGULA LONGITUBIS SP. NOV. ( Fig. 39 )

Material

Holotype: On microscopic slide, MNHN S3801 Mozambique: Bela Vista, coll. Dartevelle, 1947.

Other specimens examined: same origin: MNHN S3 MOL A 335.

Description

The specimens are spherical, the biggest 7 mm in diameter. They are entirely covered with siliceous sand. The siphons are sessile and close to each other; the oral siphon has six pointed lobes in the shape of a star. In some specimens hair-like short filaments arise from the ventral side of the body. The tunic is transparent, very thin but extremely resistant.

The thin body wall has a musculature made of well-separated ribbons ( Fig. 39C ). There are sphincters around the siphons and radiating muscular bundles that reach halfway down each side. The body also has a ventral belt of short transverse fibres ( Fig. 39C ).

The eight oral tentacles are bushy, with numerous ramifications, and they totally occlude the oral aperture. The prepharyngeal band does not form a dorsal V. The dorsal tubercle is a circular button opened posteriorly in a C-shaped slit with its horns rolled inward ( Fig. 39C ). The dorsal lamina is a short, plain edged, low membrane.

The branchial tissue is flat. There are six very low folds on each side, each with only two longitudinal vessels. There are six rows of coiled stigmata. Each infundibulum has two imbricated stigmata wound in opposite directions ( Fig. 39D ). At the endostylar end of the stigmata rows, the infundibula are doubled ( Fig. 39D ). At each extremity of a row of six infundibula crossed by the longitudinal vessels is an additional infundibulum.

The gut is particularly long ( Fig. 39A,C ). A short oesophagus leads to a wide and long stomach, which has a thin wall on which appears a mosaic pattern ( Fig. 39C ). No hepatic gland is individualized. The long and narrow intestine describes a primary loop to finally curve anteriorly and attach to the dorsal lamina ( Fig. 39C ). The edge of the anus is finely toothed. The gut is voluminous and occupies most of the left side ( Fig. 39A ).

A single massive and elongated hermaphroditic gonad lies in the middle of the right side ( Fig. 39B,C ). The testis covers a central ovary. The genital papillae are short; the female papilla is distal, and the male papilla opens a little behind it ( Fig. 39C ). The voluminous renal vesicle is applied to the whole posterior length of the gonad ( Fig. 39B,C ).

The gut, the gonad and the kidney are very loosely attached to the body wall.

Remarks

This new species has several uncommon characters: branchial folds made of only two longitudinal vessels, a particularly long intestine folded in a double loop, and a single gonad on the right side.

In the Mozambican region, two other Molgula species with two longitudinal branchial vessel per fold have been recorded: Molgula brieni Monniot C. & Monniot F., 1976 and Molgula dicosta Millar, 1988 . Both have one gonad on each side of the body.

Etymology

The species name recalls the particularly long intestine.

Figures

Figure 39. Molgula longitubis sp. nov.: A,B, both sides in external view. C, body ventrally opened. D, part of the branchial tissue close to the endostyle. Scale bars: A,B,C = 5 mm, D = 0.5 mm.