Aplidium breviventer, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 204-205

Aplidium breviventer n. sp.

( Figs 1A, B ; 112A )

TYPE MATERIAL. — Federated States of Micronesia. Pohnpei, NE lagoon, Tehpehk Island, bath sponge farm growing on nylon line, 6°57.68’N, 158°17.85’E, 8 m, 15.X.1996 ( MNHN A1 APL.B 389).

ETYMOLOGY. — From the Latin brevis: short, and venter: abdomen.

DESCRIPTION

The peach-coloured colonies are soft, lobed, very inflated underwater ( Fig. 112A ). The common cloacal apertures protrude in chimneys at the cloacal channel crossings. These channels are visible from the colony surface, as the tunic above them is transparent. The zooids are irregularly lined up along these channels.

The zooids have a wide thorax, a short abdomen that is narrower than the thorax, and a short post-abdomen separated by a narrow section below the bottom of the gut loop. The oral siphon has six small lobes. The cloacal aperture is wide, opening the branchial sac from the second to the fourth stigmata row ( Fig. 1A ). The languet is large and clearly planted above the rim of the cloacal siphon. There are 12 short and stout tentacles in two orders. The branchial sac has nine to ten rows of stigmata, which are not interrupted on the dorsal line. There are at least 25 stigmata in a row on each side. The most posterior rapheal languets are much displaced on the left side. The thoracic muscles are thinly spaced bundles, of a sinuous design and often anastomosed.

The thorax narrows abruptly behind the branchial sac and the oesophagus opening projects inside the branchial cavity. The oesophagus is extremely short. The spherical stomach has an irregularly folded wall, in some zooids with almost entire longitudinal ridges ( Fig. 1A ), while in others the folds are so cut in pieces that the stomach seems areolated ( Fig. 1A ). A transverse section shows 20 to 24 folds. The post-stomach and mid-intestine are very short. The anus opens at the level of the fifth or sixth stigmata row.

The post-abdomen ( Fig. 1A ) is no longer than the thorax when the gonads are fully developed. It begins with a short and narrow segment and progressively widens. The testis follicles number about 50 in a cluster placed against and behind the ovary. The gonads leave only restricted space for the terminal heart (not shown).

Five to six larvae are incubated inside the wide cloacal cavity. The most advanced ones have already an uncoiled tail and a thick tunic. The spherical trunk measures 0.9 mm in diameter; four rows of numerous stigmata are clearly visible ( Fig. 1B ). The three adhesive papillae are well-spaced on long, thin stems. Round ampullae are distributed in four anterior median groups alternating with the adhesive papillae. There are also two or three of these ampullae on the posterior ventral side of the larvae ( Fig. 1B ). The tail does not exceed half a turn around the trunk.

REMARKS

This species is very similar to A. altarium ( Sluiter, 1909) , the type of which we examined (ZMA TU 176) ( Fig. 1C ). Sluiter’s specimen is a small pedunculate colony. The post-abdomen of the zooids in that species is identical to ours but its cloacal aperture is more anterior than ours, with a languet prolonging the siphon’s rim. Its larvae are smaller; they have three adhesive vesicles lying well apart from each other, but these are separated in A. altarium by only four pairs of ampullae ( Fig. 1C ). Its stomach folds are numerous and entire. Millar’s (1956) description of A. altarium is not precise but corresponds fairly closely to Sluiter’s type.

The description that Kott (1992a) gave for A. altarium may correspond to several species of different colours. Kott also noted larval incubation either in the cloacal cavity or in a pedunculate pouch. Her figure of the larva shows more vesicles than Sluiter’s specimen.

A. breviventer n. sp. differs from A. sacciferum n. sp. in the mode of incubation, the folds of the stomach, and the number of ampullae between the larval adhesive papillae.

Figures

FIG. 1. — A, B, Aplidium breviventer n. sp.; A, zooid; B, larva; C, Aplidium altarium (Sluiter, 1909), larva. Scale bars: A, 1 mm; B, C, 0.5 mm.

FIG. 112. — A, Aplidium breviventer n. sp.; B, Aplidium cerebrum n. sp.; C, Aplidium intextum n. sp.; D, Aplidium longithorax Monniot F., 1987; E, Aplidium macrolobatum Kott, 1992; F, Aplidium nadaense (Nishikawa, 1980).