Didemnum pellucidum Kott, 2001

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 : 2450-2451

Didemnum pellucidum Kott, 2001

( Figure 20H )

Didemnum pellucidum Kott 2001, p 222 .

Distribution

Previously recorded (see Kott 2001): Western Australia (Rottnest I., Yallingup); South Australia (Yorke Peninsula, Eyre Peninsula, Gulf St Vincent, Kangaroo I.). New record: Tasmania (Eve Point, Bathurst Channel, SAM E3271 ) .

Description

Delicate, translucent, encrusting colony with spicules largely confined to a sparse but even layer in the surface and another thin layer on the base of the colony. Rare but large, circular, sessile common cloacal apertures are randomly distributed. In life, the newly recorded colony is a pinkish white colour and resembles colonies of Diplosoma translucidum . Deep primary common cloacal canals continue into extensive horizontal posterior abdominal cavities separating the basal test from the zooid-bearing surface layer through which long cylindrical branchial siphons extend to the surface. Spicules are stellate, all with 9–11 conical rays in optical transverse section but they are very variable in size, smaller spicules to 0.03 mm diameter being found in patches and scattered amongst the less common larger ones which are to 0.1 mm diameter. Zooids are characteristically small with a fine retractor muscle, long cylindrical branchial siphon and have a sessile, open atrial aperture without an anterior tongue. In the newly recorded specimen they are in vegetative stage with oesophageal buds and lack gonads.

Remarks

This temperate species is readily distinguished by the two size-groups of stellate spicules and their distribution, the small zooids and the soft colonies with large circular common cloacal apertures. The newly recorded colony appears to be a pinkish white colour that contrasts with the various shades of pink to red previously recorded (see Kott 2001).

Figures

Figure 20. In situ images of: (A) Didemnum fragum (SAM E3266); (B) Didemnum fuscum (QM G308730); (C) Didemnum incanum (SAM E3252); (D) Didemnum jucundum (SAM E3236); (E) Didemnum leopardus (QM G308719, holotype); (F) Didemnum microthoracicum (SAM E3256); (G) Didemnum moseleyi (QM G308713); (H) Didemnum pellucidum (SAM E3271).