Didemnum biglutinum Monniot F. 1995

Monniot, Françoise, 2010, Some new data on tropical western Pacific Ascidians, Zootaxa 2561 (1), pp. 1-29 : 5-6

Didemnum biglutinum Monniot F. 1995

( Figure 2C–D , 5, 6 )

Didemnum biglutinum Monniot F., 1995:300 Fig.1, pls 1A, III D. Monniot F. & Monniot C.: 1996 152 Fig. 9 C , pl. 2D; 2001:266.

Material. coll. Coral Reef Research Foundation. Palau, Koror, Ngermeaus channel, 07°11.65’N – 134°22.65’E, 18m, 28/VII/2007, 0CDN 9581-X ( MNHN A2 DID. C 601 ) . Papua New Guinea, New Hanover, Nusandaul Isl. , 02°37.30’S – 150°28.78’E, 11m, 03/VII/2003, 0CDN 9049-U ( MNHN A2 DID. C 529 ) . Maldives, N. Male Atoll, 04°11.43’N – 73°25.05’E, 23m, 22/IX/997, 0CDN 5316 ( MNHN A2 DID. C 458 ) .

The colonies are flexible sheets of varied colours: white, yellow, brown or purple, with often two different colours in a same colony ( Fig. 2C–D ). The colony surface is smooth due to a thin layer of tunic without spicules. The common cloacal apertures are numerous raised in short chimneys. The spicules 20 to 30µm in diameter are balls composed of numerous rods ( Fig. 5) and are dense in the whole colony thickness; clumps of pigment cells are located in the basal layer. The common cloacal cavity extends at the thoracic level. In formalin the zooids and larvae are brown. The oral siphon is short. The atrial aperture uncovers a large part of the branchial sac and is devoid of a languet. The lateral thoracic organs are ear-shaped, vertical above the fourth stigmata row ( Fig. 6B ). The muscular appendage is attached for the most of the length of the oesophagus. Abdomen and thorax are about the same length: 0.5mm. A single testis lobe protrudes from the base of the gut loop with 8 to 9 turns of the sperm duct The larval trunk 0.5mm in length has 2 divergent adhesive papillae edged with 4 long vesicles on each side ( Fig. 6A ).. They are not gemmiparous.

Remarks. Didemnum biglutinum is widely distributed in the Pacific and Indian oceans. Specimens from all stations have the same colony structure, same zooids and larvae. Kott (2001) synonymized D. biglutinum with D. albopunctatum ( Sluiter, 1909) .The specimens that she describes, however, differ in having an atrial languet and a common cloacal cavity which penetrates below the zooid abdomens. The larvae are said to have 4 pairs of lateral ampullae, but have more in her figure (Fig.69C). Sluiter’s description is very short, gonads and larvae are not mentioned. I have examined Sluiter’s material which corresponds to several species. Kott (1981) established a lectotype for a sample labelled ZMA TU 4433 in the Amsterdam Museum, but her statement is based only on the spicule shape, this colony having no gonads and no larvae.Thus even the genus identification must remain doubtful. Kott (2004:52; 2004:2488; 2005:61; 2007:1176) has identified several didemnids as D. albopunctatum , but did not describe gonads and larvae.

Consequently I do not retain the synonymy proposed by Kott, based solely on the spicule shape.

Figures

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

FIGURE 6. Didemnum biglutinum: A: abdomen, B: thorax, C: larva. Scale bars: A=0.2mm, B–C=0.5mm.

FIGURE 9. Didemnum nocturnum: A: thorax, B: abdomen. Scale bar 0.5mm.