Didemnum madeleinae, Monniot & Monniot, 2001

Monniot, Françoise & Monniot, Claude, 2001, Ascidians from the tropical western Pacific, Zoosystema 23 (2), pp. 201-383 : 268-270

Didemnum madeleinae n. sp.

( Figs 53 ; 54A ; 120D )

TYPE MATERIAL. — Papua New Guinea. Louisiade Archipelago, Deboyne Lagoon, Nivani Island, overhang, 10°47.46’S, 152°23.08’E, 10 m, 30. V.1998 ( MNHN A2 DID.C 470).

ETYMOLOGY. — Named after Madeleine Martin, who helped in the preparation of this paper.

DESCRIPTION

The orange colonies ( Fig. 120D ) form large crusts 2 mm thick that are easy to remove from the substrate. The surface is smooth with many small common cloacal apertures, which appear white in life: the orange pigment is superficial and disappears in formalin. The consistency is hard, as spicules are dense throughout the colony. The cloacal channels are wide but limited to the thoracic layer of the colony. Some accumulations of orange inclusions lie in the basal layer of the colony. The oral siphon with six sharp lobes, has the shape of a funnel with a basal sphincter ( Fig. 53A ). There is no cloacal languet. The cloacal aperture is wide and uncovers most of the four stigmata rows ( Fig. 53A ). The round and small lateral thoracic organs are near the edge of the cloacal aperture at the level of the third transverse vessel.

The oesophageal peduncle is long and the retractor muscle that parts from it lies against the abdomen ( Fig. 53A ).

The abdomen ( Fig. 53B ) has about the same size as the thorax. The gut loop is slightly twisted. The single testis follicle with seven turns of the sperm duct is located inside the gut loop, beside a very large oocyte ( Fig. 53B ).

The rather spherical larvae ( Fig. 53C ) are incubated in the densely spiculated basal layer of the colony. Their trunk measures 1 mm but the larvae are not gemmiparous. They have three adhesive papillae, and about 12 short digitiform ampullae on each side. The tail is wound in three quarter of a turn around the trunk.

The spicules ( Fig. 54A ) are stellate with rather few conical pointed rays: they measure up to 50 µm across.

REMARKS

D. madeleinae n. sp. is some characters in common with Didemnum captivum Monniot F. & Monniot C., 1999 known only from Tanzania: the orange colour, the shape and size of the spicules, the position of the lateral thoracic organs and the retractor muscle, and the structure of the abdomen. But the shape of the oral siphon and the cloacal aperture are very different, and the larvae are very different in size. These characters and the geographical distance of this record from Tanzania argue persuasively against a synonymy.

All other Didemnum Savigny, 1816 species with only one testis follicle, without cloacal languet, and with a larva that has numerous anterior ampullae – all other such species have a very dark pigment and different spicules from this new one.

Figures

FIG. 53. — Didemnum madeleinae n. sp.; A, thorax; B, abdomen; C, larva. Scale bar: 0.5 mm.

FIG. 54. — Spicules; A, Didemnum madeleinae n. sp.; B, Polysyncraton adelon n. sp. Scale bars: 10 µm.

FIG. 120. — A, Didemnum algasedens n. sp.; B, Didemnum cuculliferum (Sluiter, 1909); C, Didemnum lacertosum Monniot F., 1995; D, Didemnum madeleinae n. sp.; E, Didemnum obscurum Monniot F., 1969; F, Didemnum rodriguesi Rocha & Monniot F., 1993.