Monniotus papillosus, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 221-223

Monniotus papillosus n. sp.

( Figs 15 ; 114A )

TYPE MATERIAL. — Papua New Guinea. Milne Bay Province, East Cape, Boia Boia Waga Island, in cave, 10°12.26’S, 150°44.75’E, 25 m, 27. V.1998 ( MNHN A1 MON 2).

ETYMOLOGY. — From the Latin papillosus : with papillae.

DESCRIPTION

The colony is made of sand-covered branched lobes, each ending in an enlarged tip and containing only one zooid ( Fig. 114A ). Each zooid’s thorax and abdomen and a part of its post-abdomen are in a lobe: the very thin posteri- or part of its post-abdomen lies in the narrow basal erect branches of the colony.

The zooids are very elongated ( Fig. 15A, B, D, E ), with the 6 mm thorax longer than the 3 mm abdomen. The post-abdomen is of variable length, shorter when the ovary is developed and particularly long when the zooids have only mature testis follicles, at which time it can reach 18 mm.

Both siphons open at the same level, and in life have red pigment on their rim. Each has six pointed lobes. The oral siphon curves to the ventral side.

The body wall is thin and transparent. The thoracic musculature is mostly transverse with regularly spaced fibres. The longitudinal muscles are thinner, prolonged down to the posterior extremity of the post-abdomen.

The oral tentacles are in three orders of size at the base of a velum. The dorsal tubercle opens as a transverse slit. The branchial sac has very elongat- ed stigmata. The rows are difficult to count as parastigmatic vessels are anteriorly transformed into true transverse vessels while posteriorly the stigmata remain continuous under the vessels. Numerous papillae arise from the transverse and parastigmatic vessels ( Fig. 15F ). We counted 17 languets along the dorsal lamina and about 30 stigmata per half-row in the middle of the branchial sac.

The anus opens at the mid-level of the thorax. The gut forms a straight, closed loop ( Fig. 15A, C ). The oesophagus is short and narrow. The stomach is elongatedly cylindrical; its wall is smooth against the intestine and has eight folds, some of them interrupted, on the opposite side ( Fig. 15C ). There is a post-stomach widened in a ring, and a mid-intestine separated by a narrowing from the posterior intestine, which begins with caeca.

When fully developed, the gonads occupy a large part of the long post-abdomen ( Fig. 15B, D ). The ovary is at some distance from the gut, immediately followed by a double row of very numerous testis follicles. Behind the testis is the heart, and the post-abdomen then extends posteriorly as a very thin thread with two or three terminal branches ( Fig. 15E ). No larvae were present in the colony.

REMARKS

This species differs from M. ramosus Millar, 1988 in the shape of the stomach, and the number of branchial papillae. The gonads of M. ramosus are unknown. The shape of the oral siphon is the same in both species.

M. australis Kott, 1957 has only one branchial papilla on each transverse vessel, and the testis is not elongated. M. radiatus Kott, 1992 has only nine stigmata rows, a stomach with 12 folds, and bunched testis follicles.

Mo. pacificus n. sp. essentially differs from the other Monniotus species in its areolated stomach.

Figures

FIG. 15. — Monniotus papillosus n. sp.; A, B, two parts of a zooid; C, abdomen; D, E, two parts of a zooid; F, part of a branchial sac. Scale bars: A-E, 2 mm; F, 0.5 mm.

FIG. 114. — A, Monniotus papillosus n. sp.; B, Polyclinum psammiferum Hartmeyer, 1911; C, Pseudodistoma aureum (Brewin, 1957); D, Pseudodistoma digitata n. sp.; E, Pseudodistoma fragile Tokioka, 1958; F, Pseudodistoma novaezelandiae (Brewin, 1950).