Aplidium cerebrum, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 205-207

Aplidium cerebrum n. sp.

( Figs 2 ; 112B )

Aplidium sp. A Monniot F. & Monniot C. 1996: 140, fig. 3A, B, pl. 1E. Type locality: Papua New Guinea.

TYPE MATERIAL. — Papua New Guinea. Coral Sea, eastern Fields, overhang, 10°09.35’S, 145°33.92’E, 27 m, 15. VI.1998 ( MNHN A1 APL.B 412).

ETYMOLOGY. — From the Latin cerebrum : brain.

OTHER MATERIAL EXAMINED. — Philippines. Sulu Sea, Pasig Shoal, on rock, 9°57.16’N, 119°21.30’E, 11 m, 23.IV.1995 (MNHN A1 APL.B 387).

Papua New Guinea. Coral Sea, eastern Fields, overhang, 10°02.22’S, 145°33.01’E, 23 m, 14. VI.1998 ( MNHN A1 APL.B 413).

DESCRIPTION

The colonies are soft, low cushions with zooids arranged in double rows around irregular bulges of tunic ( Fig. 112B ). There are just a few common cloacal apertures on short, transparent chimneys. The colour in life is highly variable from light blue to orange and brown. The formalin preserved colonies are brown. There is some surface sand at the level of the cloacal channels or else no incrustation at all. The thoraces are perpendicular to the colony surface but the postabdomens extend in all directions. The zooids are up to 8 mm long and very thin. The oral siphon has six lobes. The narrow cloacal siphon is a simple hole at the third or fourth row of stigmata. The cloacal languet is either simple or ends in two lobes. It arises distinctly anterior to the cloacal opening ( Fig. 2A ).

The branchial sac has 12 to 15 rows of stigmata, which do not reach the endostyle. The abdomen ( Fig. 2A ) forms a long loop with an elongated stomach cut in five deep folds, without an annular post-stomach but with a narrow segment giving way to a slightly enlarged mid-intestine. Caeca are at the posterior pole of the gut loop ( Fig. 2A ).

The gonads are far from the gut in the second half of the post-abdomen ( Fig. 2B, C ) or farther, close to the heart. The ovary is immediately followed by tightly packed testis follicles.

One or two larvae ( Fig. 2D ) are incubated in the cloacal cavity. The trunk measures 0.5 mm. There are three adhesive papillae on thin stems with intermediate odd, short protrusions and an anterior crown of not very well-individualised ampullae on each side ( Fig. 2D ).

REMARKS

The appearance of colonies, as well as the zooid distribution in them, the location of the cloacal languet at some distance from the cloacal aperture, and the stomach with five folds all recall Aplidium lenticulum Kott, 1992 . The species differs in the small amount of adhering sand, when present at all, in the smaller size of its zooids, and in the absence of granular inclusions in the tunic. Aplidium cellis Monniot F., 1987 has a similar general structure but in that species the cloacal languet emerges from the very rim of the cloacal aperture.

This species corresponds to the species described as Aplidium sp. A by Monniot F. & Monniot C. (1996) from Papua New Guinea. The species name refers to the brain-like structure of the colony.

Figures

FIG. 2. — Aplidium cerebrum n. sp.; A, B, two parts of a zooid; C, post-abdomen; D, larva. Scale bars: A-C, 1 mm; D, 0.25 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).