Didemnum perplexum Kott, 2001

Kott, Patricia, 2004, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (part I), Journal of Natural History 38 (19), pp. 731-774 : 757-758

Didemnum perplexum Kott, 2001

( figure 14 )

Didemnum perplexum Kott, 2001: 224 and synonymy.

Distribution. New record: Queensland (Big Broadhurst Reef, QM GH5350). Previously recorded (see Kott, 2001): Queensland (Capricorn Group, Swain Reefs), New Caledonia, Indonesia.

Description. In preservative, the colony is a hard white sheet. The stellate branchial apertures are lined with spicules, which are crowded throughout the colony. They are stellate to 0.05 mm diameter, with five to seven, and occasionally nine, robust conical rays in optical transverse section. The ray length / spicule diameter ratio is 0.4, the common cloacal cavity is a large horizontal space with thoraces crossing it, either separately with a ventral strip of test, or in groups of two or three clustered around a common test connective, each presenting the wide, sessile, dorsal atrial aperture to the surrounding common cloacal cavity. A small atrial lip projects from the upper rim of the aperture. Abdomina are embedded in the hard basal layer of test. Nine stigmata are in the anterior row and seven in the posterior row. A retractor muscle projects posteriorly from half to three-quarters of the way down the oesophageal neck. The post-pyloric part of the gut loop is bent ventrally to form a double loop. Oesophageal buds are present but neither zooids nor embryos were detected.

Remarks. The moderate-sized stellate spicules with relatively few rays resemble, but are larger than, those of the temperate species D. incanum ( Herdman, 1899) which has smaller zooids with fewer stigmata.

One more stigmata per row has been detected in the newly recorded zooids than previously reported for this species. Other characters, the robust zooids with a fine retractor muscle and double gut loop, a horizontal common cloacal cavity and sturdy stellate spicules with relatively long rays, occur in all examined specimens (see Kott, 2001).

Figures

FIG. 14. Didemnum perplexum (QM GH5350): (A, B) spicules.