Didemnum corium, Kott, 2005

Kott, Patricia, 2005, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (Part 3), Journal of Natural History 39 (26), pp. 2409-2479 : 2440

Didemnum corium sp. nov.

( Figures 6C,D, 15F , 19G )

Distribution

Type locality: Tasmania ( Port Davey , Bathurst Channel, Beebee Point, 6–8 m on silt, coll. K. Gowlett Holmes, 12 March 2003, holotype SAM E3249 ) .

Description

In preservative, the colony is a circular grey slab, the colour resulting from black faecal pellets mixed with white spicules. A few sessile common cloacal apertures are on the surface and occasionally these seem to be extended into large openings extending along one of the common cloacal canals. This is apparent only and results from the absence of spicules or other test inclusions in the thin roof of the common cloacal canal. Spicules are evenly distributed in the surface and on the base of the colony and in the lining of the deep primary and posterior abdominal common cloacal cavities. They are large, to 0.1 mm diameter and have seven to nine robust pointed rays in optical transverse section. Thoraces are clumped together and are surrounded by the primary common cloacal cavities but the abdomina are embedded in the basal test. Sometimes the primary common cloacal cavities penetrate the clump of thoraces, separating them from one another in independent spicule-filled test sheaths. Some debris is embedded in the basal test. In life, colonies are white cushions with large common cloacal apertures around the margin.

Zooids are small with a fine tapering retractor muscle. The atrial opening is wide but lacks any atrial lip. Four or five vascular stolons project into the test from the concave ventral aspect of the gut loop. The colony is in vegetative phase, with oesophageal buds. Gonads were not detected.

Remarks

The species is distinguished by its large spicules with relatively few rays in optical transverse section and their absence from some parts of the colony. Didemnum microthoracicum Kott, 2001 has similar spicules but they are crowded throughout the colony rather than being confined to certain layers as they are in the present species; and it has a quilted pattern on the colony surface.

Figures

Figure 15. Scanning electron micrographs of the calcareous spicules of: (A) Polysyncraton millepore (WAM 122.93); (B) Polysyncraton orbiculum (WAM 128.90); (C) Polysyncraton papyrus (SAM E3253); (D) Didemnum astrum (WAM 601.89); (E) Didemnum cilicium sp. nov. (SAM E3251, holotype); (F) Didemnum corium sp. nov. (SAM E3249, holotype); (G) Didemnum cygnuus (QM G308716); (H) Didemnum fragum (SAM E3266).

Figure 19. In situ images of: (A) Polysyncraton glaucum (QM G308736); (B) Polysyncraton papyrus (SAM E3253); (C) Polysyncraton pedunculatum (SAM E3272); (D) Polysyncraton purou (QM G308707); (E) Polysyncraton rica (SAM E3245); (F) Didemnum cilicium (SAM E3251, holotype); (G) Didemnum corium (SAM E3249, holotype); (H) Didemnum cygnuus (QM G308716).