Monniotus pacificus, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 220-221

Monniotus pacificus n. sp.

( Figs 14 ; 113F)

TYPE MATERIAL. — Palau. Koror, Uchelbeluu Reef, W side, on wall, 7°16.41’N, 134°31.43’E, 72 m, 11.VIII.1997 ( MNHN A1 MON 1).

ETYMOLOGY. — From the Pacific Ocean.

DESCRIPTION

The colonies are large masses, 5 cm in diameter, with erect zooids isolated for almost their whole length on branch-like lobes (Fig. 113F). The tunic is thin, colourless, and impregnated with sand. The zooids are elongated ( Fig. 14A ). Both siphons are terminal and at the same level, at the anterior corners of the zooids. Each lobe reaches 4.5 cm in length and a maximum diameter of 0.8 mm at its free end.

In some parts of the colony the branches are ramified, some zooids arising from the postabdomens of other zooids.

Out of the tunic, the siphons are red. The oral siphon has five red teeth and a flat colourless dorsal lobe. The cloacal siphon has six pointed teeth. The body wall is strongly muscular with longitudinal and transverse fibres. The longitudinal muscles extend posteriorly along the whole length of the post-abdomen. There is a velum before the ring of oral tentacles, which are in three orders of size. The dorsal tubercle opens in a transverse slit. The branchial sac has 20 rows of about 40 narrow and elongated stigmata on each side. The dorsal lamina has 19 pointed languets increasing in size posteriorly. Each transverse vessel bears large erect languets, pressed against each other in the posterior part of the branchial sac. These languets are less numerous and shorter on the secondary transverse vessels.

The abdomen is shorter than the thorax ( Fig. 14 A-C) but the animals examined are strongly contracted. The oesophagus is narrow. The stomach is wide and elongated, barrel-like with either low ridges or lines of areolations ( Fig. 14C ). The other parts of the digestive tract are similar to those in the genus Aplidium including an annular post-stomach and rectal caeca.

The post-abdomen is particularly long, inflated in the anterior part and progressively thinner posteriorly ( Fig. 14A, B ). The zooids are not fully mature. Only some very small round testis follicles are aligned in the anterior part of the postabdomen ( Fig. 14C ). The heart lies in the middle of the post-abdomen. Neither ovary nor larvae were present in the specimens examined.

REMARKS

Kott (1992a) created the family Pseudodistomidae for two genera: Pseudodistoma Michaelsen, 1924 and Anadistoma Kott, 1992 . They only differ from other genera placed in the family Polyclinidae in having only three rows of stigmata. In our opinion this does not justify a new family. Another new family, the Protopolyclinidae Kott, 1992 includes three genera rather different from each other, and among them Monniotus Millar, 1988 . We do not follow this opinion considering that the characters separating the three genera are more important than those differentiating them from the Polyclinidae .

This species differs from the four other Monniotus species in having an areolated stomach wall instead of one with a few longitudinal ridges. The colonies look like those of M. ramosus Millar, 1988 from Mozambique, which has ramified branches but different siphons, less numerous stigmata, and fewer branchial papillae.

M. australis (Kott, 1957) from southern and western Australia has only 10 rows of stigmata and a single papilla on each transverse vessel.

M. radiatus Kott, 1992 from Victoria and New South Wales has nine rows of 20 stigmata cut by parastigmatic vessels and only 10 papillae on each of the transverse vessels.

Mo. pacificus n. sp. and M. papillosus n. sp. are the first species of Monniotus described from the northern hemisphere.

Figures

FIG. 14. — Monniotus pacificus n. sp.; A, B, zooids; C, abdomen and post-abdomen. Scale bars: 2 mm.