Trididemnum lanugineum, Monniot, 2010

Monniot, Françoise, 2010, Some new data on tropical western Pacific Ascidians, Zootaxa 2561 (1), pp. 1-29 : 4-5

Trididemnum lanugineum n. sp.

( Figures 2B , 3, 4 )

Material. Palau, coll. Coral Reef Research Foundation, Koror, SW Ngeruktabel, 07°14.83’N – 134°21.12’E, 10m, cavern, 01/ VI /2008, 0CDN9584-A ( MNHN A2 TRI 188 ) .

The white colonies ( Fig.2A ) are crusts several centimetres in extent with round edges and a raspy surface. In formalin the thickness is about 2mm, in 3 layers. The surface layer is hard, filled with large spicules 170µm in diameter with numerous sharp rays ( Fig. 3), and contains the oral siphons. The thoraces are grouped in pillars of tunic linked to the medium spicule-free layer of tunic that has a cotton-wool texture. Abdomens and larvae are enclosed in this soft but very resistant layer. The basal part of the colony is densely filled with spiny spicules. At the contact with the substrate, the spicules are almost balls with very short rays. The oral siphon is trumpet-like with a plain rim, very often broken during the dissection. The cloacal aperture has a wide horseshoe shape. Its dorsal side is covered by a long languet applied on the dorsal lamina ( Fig. 4B ); the circular lateral thoracic organs protrude from its margin. The branchial sac has 3 rows of long stigmata: 7 were counted in the first two rows and 6 in the third row per side. A muscular appendage was not found. The abdomen ( Fig.4A ) is smaller than the thorax. The gut loop is included into an opaque tissue. The single testis vesicle is placed above the bend of the intestine circled with 4 (rarely 5) turns of the sperm duct.

Several larvae were found into the cotton-like layer of the colony, they do not seem totally developed. The tail is wound in ¾ of a turn around a trunk 0.85 to 1mm long ( Fig. 4C ). The 3 adhesive papillae have parallel stems. On each side, at their base are 4 round vesicles, obviously incompletely formed lateral ampullae. The internal structure is obscured by large opaque cells filling the larval body wall (partly figured Fig. 4C ). Ocellus and otolith lie in a clear dorsal vesicle. The anterior part of a damaged larva, found in shreds of tunic, has 3 adhesive papillae and 8 lateral vesicles on each side, suggesting that these vesicles may divide at maturity.

The originality of this new species consists in the unique structure of the atrial opening, widely open with a large dorsal languet and very large spicules.

Figures

FIGURE 2. A:Trididemnum cyclops. B: Trididemnum lanugineum n. sp. C: Trididemnum biglutinum from New Guinea. D: Trididemnum biglutinum from Palau.

FIGURE 4. Trididemnum lanugineum n. sp.: A: abdomen of a zooid, B: thorax, C: larva. Scale bars: 0.5mm.