Didemnum tantulum, Kott, 2007

Kott, Patricia, 2007, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (part 4), Journal of Natural History 41 (17 - 20), pp. 1163-1211 : 1190-1192

Didemnum tantulum sp. nov.

( Figures 4 A–C, 10D)

Distribution

Type locality: Queensland (Great Barrier Reef: 17.855 ° S, 146.585 ° E, 43 m, 26 September 2003, holotype QM G308890 ) .

Description

Colonies are lumpy, encrusting and overgrowing coral rubble, with large black pigment cells in the base of the colony and occasional small patches in the surface, but not in the middle layer (around the zooids). Colonies have a quilted surface owing to the deep circular common cloacal canals that surround large clumps of zooids. Primary common cloacal canals are deep but not posterior abdominal. Spicules are in the surface test, become sparse around the zooids, and are absent from the central and basal test. The spicules (to 0.035 mm diameter) are burr-like with 15–17 long, crowded rays in optical transverse section. The ray tips are conical or irregular. Zooids have thoraces with a rather rectangular outline, a long, fine retractor muscle, a large, sessile atrial aperture and a long branchial siphon. They have nine coils of the vas deferens and an undivided testis. The large larvae (1.0 mm long trunk) have eight pairs of ectodermal ampullae, one blastozooid and three deep tulip-shaped anteromedian adhesive organs on long stalks. The cerebral vesicle projects up from the upper surface of the larval thorax.

Remarks

The spicules and the zooids with nine coils of the vas deferens resemble those of D. hiopaa C. and F. Monniot, 1987, but the larvae are larger with more ampullae and a blastozooid. Spicules also are like D. tabulatum but are significantly smaller and the present species has more coils of the vas deferens. The larva of D. tabulatum has not been described.

Didemnum fibriae Kott, 2004a from Cockburn Sound (WA) has similar, but larger, spicules and a similar large larva with a blastozooid. However, it has more (11) vas deferens coils that, with its fewer spicule rays, distinguish it from the present species.

Didemnum υesica sp. nov., D. jedanense , and D. parau have rod-like rather than the long, pointed or irregularly tipped spicule rays of the present species, and D. υesica has bladder cells in a superficial layer and in the test, and black pigment cells mostly around the zooids rather than in the base of the colony as in the present species.

The small spicules and their distribution, nine coils of the vas deferens and the large number (eight pairs) of larval ectodermal ampullae are the principal characteristics of this species.

Figures

Figure 4. (A–C) Didemnum tantulum (QM G308890, holotype): (A) thorax; (B) abdomen; (C) larva. (D) Didemnum υesica (QM G308874, holotype): zooid. Scale bars: 0.1 mm.