Didemnum

Monniot, Françoise, 2009, Some ascidians from Indonesian marine lakes (Raja Ampat Islands, West Papua), Zootaxa 2106, pp. 13-40 : 18

Didemnum sp. 2

( Figures 5 A,B,C – 6A)

Material. Indonesia. West Papua, Gam Island, Danau A Gam marine lake, 00°26.518’S – 130°41.134’E, 0.25m, 23/XI/2007, coll. L.J. Bell and L.E. Martin, DAG 0 59 ( MNHN A2 DID.C 590).

A single colony 4cm long and 0.5mm thick was of a cream colour in life ( Fig. 6A ), coating a bivalve shell. Its surface has a pattern in pavement, each system of zooids with a central common aperture. Spicules and round pigment cells are mixed at the tunic surface. The common cloacal cavity extends at the thoracic level and contains fecal pellets. The abdomens are included in the basal tunic filled with spicules. The zooids 8mm in length have 6 long, thin oral lobes ( Fig. 5 B) contrasting with the contracted thorax. There is no languet above the wide atrial aperture. The lateral thoracic organs are leaf-shaped, very protruding ( Fig. 5 B). The stigmata could not be counted. The waist is short with a retractor muscle as long as the thorax. The digestive loop ( Fig. 5 C) is slightly twisted with a short stomach, a wide post-stomach and the intestine is divided in compartments. The single testis vesicle ( Fig. 5 C) is circled with 5 to 6 turns of the sperm duct. An oocyte is present in many zooids of the colony but no larvae were detected. The spicules ( Fig. 5 A) are regularly stellate up to 40µm in diameter, mixed with smaller ones. Large spicules of 60µm are rather common, with the same shape. The short rays have a hexagonal base.

Didemnum sp.2 shares characters with Didemnum digestum Sluiter, 1909 and Didemnum uturoa Monniot & Monniot, 1987 . These two species have particularly long oral lobes, but the shape of their spicules clearly differs in having one or several long rays among short ones. D. digestum has a single testis vesicle in the colony from Raja Ampat, while D. uturoa has 2 testis lobes. Didemnum sp. 2 may be a new species characterized by its spicules with few short rays of equal length, its long thin oral lobes, but without larvae and a single colony it does not seem wise to create a new species.

Figures

FIGURE 5. Didemnum sp. 2, A, spicules; B, thorax; C, abdomen. Scale bar: A, B = 0.2 mm.

FIGURE 6. A, Didemnum sp. 2. B, Didemnum sp. 3.