Didemnum perplexum Kott, 2001

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 : 1189

Didemnum perplexum Kott, 2001

( Figure 9G )

Didemnum perplexum Kott 2001, p 224 and synonymy; 2004a, p 757 and synonymy.

Distribution

Previously recorded (see Kott 2004a): Queensland Capricorn Group, Swain Reefs, Big Bradhurst Reef); New Caledonia; Indonesia (Great Barrier Reef: 17.275 ° S, 146.345 ° E, 13 m; 16.705 ° S, 146.125 ° E, 34 m, QM G308860 ; 18.275 ° S, 146.455 ° E, 29 m, QM G308863 ) .

Description

Generally, the colonies are irregular scraps of encrusting sheets with thoracic common cloacal cavities. Spicules are crowded throughout and usually are up to 0.05 mm diameter, although occasionally some larger ones to 0.062 mm diameter are present. They are stellate, with five to nine conical rays in optical transverse section. A fine retractor muscle projects from about halfway down the long oesophageal neck. The branchial aperture is short and trumpet-shaped and the atrial opening is sessile, without an anterior lip. About six stigmata are in a row on one side of the body.

The sturdy but immature larval trunk (present in QM G308860 , collected in September) is about 0.45 mm long with the tail wound almost the whole way around it. The lateral ampullae are not developed in these specimens although larger larvae (0.6–0.88 mm long trunk) in the holotype ( Kott 2001) have six pairs of long ampullae .

Remarks

Didemnum coralliforme and D. grande have similar spicules with long, narrow conical rays but they are larger and have more rays than those of the present species. Didemnum candidum and D. granulatum have smaller spicules. All these species are, to some extent, convergent, the colonies, zooids and larvae, as well as the spicules, being conservative and the species readily confused.

Figures

Figure 9. Scanning electron micrographs. (A) Didemnum membranceum (QM G308854); (B) Didemnum microthoracium (SAM E3259); (C) Didemnum moseleyi (QM G308866); (D) Didemnum parau (QM G308859); (E) Didemnum patulum (QM G308769); (F) Didemnum pellucidum (QM G308886); (G) Didemnum perplexum (QM G308860); (H) Didemnum psammatode (QM G308879).