Aplidium sacciferum, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 216-218

Aplidium sacciferum n. sp.

( Figs 11 ; 113C)

Aplidium altarium – Kott 1992a: 519 part, fig. 62, pl. 10c-d.

TYPE MATERIAL. — Palau. Babeldaob, SE Airai, Ngerdwais, 7°20.82’N, 134°34.35’E, 5 m, 9.IV.1997 ( MNHN A1 APL.B 402).

ETYMOLOGY. — From the Latin saccus: bag.

DESCRIPTION

The colonies are made of several joined cushions of 3 cm in maximum diameter and 1 cm in thickness. The colour is dark purple (Fig. 113C) but the pigment is localised in the tunic only, while the zooids are colourless. The cloacal channels converge at one or two common cloacal apertures in each colony. The systems are clearly apparent because each oral aperture is circled by a dark purple ring. The tunic is very soft, translucent, without sand, and contains long filiform pigment cells. The oral siphon has six pointed lobes. The long and undivided cloacal languet is inserted close to the cloacal aperture ( Fig. 11A ). The cloacal aperture is of variable diameter due to a strong sphincter.

The oral tentacles are very numerous. The branchial sac is wide with nine rows of 22 stigmata on each side. The stigmata are interrupted on the dorsal line, and the rapheal languets are slightly displaced to the left side.

The stomach is shorter dorsally than ventrally: its wall is marked with numerous narrow longitudinal folds ( Fig. 11A ). There is an annular post-stomach. The post-abdomen is short, with an anterior ovary and a cluster of testis follicles ( Fig. 11A ).

Two or three larvae are incubated in a brood pouch appended to the cloacal cavity ( Fig. 11A ). The larvae are large, 1 mm for the trunk. They have three adhesive papillae with narrow stalks, and a line of pedunculate ampullae on each side ( Fig. 11B ). A branchial sac is already developed with four rows of numerous stigmata. On each side there are two pigment flecks, one at the base of the tail and one along the ventral side.

REMARKS

These characters correspond well to the description given by Kott (1992a), for specimens having such a brood pouch, but we have not observed a bilabiate cloacal aperture in the zooids.

This species is not Aplidium altarium , whose type has been examined. In Sluiter’s species the larva has only four pairs of ampullae between the adhesive papillae ( Fig. 1C ) and the incubation takes place inside the cloacal cavity. This same situation corresponds to what Millar described in 1956 for A. altarium for Mozambique specimens. The species described by Kott (1966) under the name A. altarium has numerous ampullae between the larval adhesive papillae, but the incubation is not in an appended brood pouch; this probably corresponds to a part of the description of A. altarium by Kott (1992a).

The description of A. altarium given by Michaelsen (1919a) for specimens from Zanzibar does not mention the larvae, so its status cannot be assessed.

The distribution of Aplidium sacciferum n. sp. is probably wide in the western Pacific Ocean, as it is now recorded from Palau and Australia.

Aplidium solidum ( Herdman, 1891) ( Figs 12 ; 113D)

Psammaplidium solidum Herdman, 1891: 620 . Type locality: Australia. Synonymy and distribution: see Kott 1992a: 586, Australia. — Monniot F. & Monniot C. 1999: 14, fig. 10, pl. 2B, Tanzania.

MATERIAL EXAMINED. — Papua New Guinea. Louisiade Archipelago, Calvados Island Chain, Brooker Channel, 11°03.09’S, 152°28.62’E, 7 m, 1. VI.1998 ( MNHN A1 APL.B 409). — Milne Bay Province, East Cape, Boia Boia Waga Island, 10°12.26’S, 150°44.75’E, 16 m, 27. V.1998 (Sample: CRRF).

DESCRIPTION

The colonies are thick crusts totally embedded with sand (Fig. 113D). The common cloacal apertures open atop swellings, and they are widely open in life. The oral openings are irregularly distributed in sinuous double rows or circles. The zooids are colourless in formalin, very small, 3 mm long for the most relaxed ones, and perpendicular to the colony surface.

Zooids have six short oral lobes. The cloacal aperture is distant from the oral siphon, as a simple hole whose anterior rim carries a short, simple languet. There are 10 to 11 rows of stigmata. The gut loop is straight, with a cylindrical stomach in the middle of the descending limb. There are five stomach folds and no distinct annular post-stomach ( Fig. 12A ).

The post-abdomen is rarely longer than the abdomen in contracted zooids. The ovary lies a little below the gut, followed by rather few testis follicles ( Fig. 12A, B ) either in a line in relaxed zooids or in a cluster after contraction.

The post-abdomen ends in two horns made by the longitudinal muscular bundles ( Fig. 12B ).

The incubation of larvae takes place at the base of the thorax. The very small larvae, 0.3 mm long, have three well-separated adhesive papillae, and an anterior crescent of spherical vesicles on each side ( Fig. 12C ).

REMARKS

The shape of the colony, the very small size of the zooids, their anatomy, and the structure of the larva are characteristic.

The new collection extends the distribution of the species, which has been recorded from several places in eastern and western Australia and in Tanzania.

Figures

FIG. 11. — Aplidium sacciferum n. sp.; A, zooid; B, larva. Scale bars: A, 1 mm; B, 0.5 mm.

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. 12. — Aplidium solidum (Herdman, 1891); A, zooid; B, abdomen and post-abdomen for another zooid; C, larva. Scale bars: A, B, 0.5 mm; C, 0.3 mm.