Didemnidae

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 : 1208-1209

Didemnidae ?genus?species

( Figure 11G, H )

Distribution

Tasmanian Canyons (King I. Canyons, 241 m, QM G308888, G308900). Description

Both colonies are thin encrusting sheets and orange in life with a horizontal and thoracic common cloacal cavity. The spicules appear to be identical, being stellate, to 0.09 mm diameter with 9–11 strong robust, pointed, conical rays with their broad bases crowded toward the centre of the spicule. One colony (QM G308888) is white in preservative with thin surface test crowded with spicules, but these become sparse in the lower half of the colony. In this specimen, large vesicles displace the surface spicules in a circle around each branchial aperture. The other colony (QM G308900) is a more extensive, encrusting sheet with brownish zooids, and is flesh-coloured to brownish beige in preservative and its spicules are crowded throughout the test. The zooids have long fine retractor muscles but are mutilated and the specimen could be either Didemnum spp. or Polysyncraton spp., neither larvae nor gonads being present to reliably indicate the correct genus.

Remarks

Although Didemnum spadix Kott, 2001 has similar colonies and vesicles arranged in a circle around each branchial aperture as in one of the colonies (QM G308888). However, although the spicules are a similar shape they are never more than 0.046 mm (not 0.45 mm sic Kott 2001). Also the brown cells lying free in the test and often around zooids of Didemnum spadix were not detected in either of the present specimens. The vesicle cells in the surface test also occur in Polysyncraton orbiculum Kott, 1962 and P. circulum Kott, 1962 , although both these species have smaller differently shaped spicules, those of the latter being burr-shaped and the former having club-shaped rays.

In view of the similarity of the spicules it is posssible that these specimens are the same species at different stages of maturity. Nevertheless it is possible that the similarity of the spicules is a coincidence and that they are different. They appear not to belong to any known taxon in either Didemnum or Polysyncraton .

Figures

Figure 11. Scanning electron micrographs. (A) Trididemnum pigmentatum (QMG308842); (B) Trididemnum sibogae (QM G308893); (C) Trididemnum titanium (QM G308816); (D) Lissoclinum capsulatum (QM G308804); (E) Lissoclinum reginum (QM G308871); (F) Didemnidae?genus?species (QM G308889); (G, H) Didemnidae?genus?species [(G) QM G308888; (H) QM G308900].