Didemnum

Monniot, Françoise, 2009, Some ascidians from Indonesian marine lakes (Raja Ampat Islands, West Papua), Zootaxa 2106, pp. 13-40 : 20-22

Didemnum sp. 3

( Figures 6 B – 7A,B,C)

Material. Indonesia. West Papua, Gam Island, Danau Nine Gam marine lake, 00°26.970’S – 130°29.149’E, 0–1.5m, 04/XII/2007, coll. L.J. Bell and L.E. Martin, DNG 0 84 ( MNHN A2 DID.C 591).

Small pieces of thin encrusting colonies were red in life ( Fig. 6 B) but are white in formalin. The colony surface is spotted by the oral apertures. The oral lobes are filled with spicules in the centre of a ring of tunic with less dense spicules. The zooids are small: 0.7mm for the best relaxed zooids. The common cloacal cavity is narrow and restricted to the thoracic level. The oral lobes are triangular on a short siphon. The atrial opening is narrow without a languet ( Fig. 7 B). The lateral thoracic organs are small in the centre of each body side. The number of stigmata could not be determined in the 4 rows. The muscular appendage starts from the base of the thorax. The waist is short. The gut loop is flat with well marked segments ( Fig. 7 C). The single testis lobe lies on the side of the rectum with 5–6 turns of the sperm duct. In some zooids, an oocyte as large as the testis is present. No larvae have been found in the colonies.

The spicules ( Fig. 7 A) are spheres of different sizes, from 20 to 40µm in diameter. Their very short rays have a hexagonal base, a blunt point and are made of incompletely fused elements. This spicule shape is not common in the genus Didemnum but alone, it cannot lead to a species identification in the absence of larvae in the colony and with no unique characters of the zooids.

Figures

FIGURE 7. Didemnum sp. 3: A, spicules; B, thorax; C, abdomen. Scale bars: A = 10 µm, B, C = 0.2 mm.

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