Didemnum patulum ( Herdman, 1899 )

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 : 1187-1188

Didemnum patulum ( Herdman, 1899)

( Figure 9E )

Leptoclinum patulum Herdman 1899, p 92 .

Didemnum patulum: Kott 2001, p 219 and synonymy;? 2005a, p 2450 and synonymy. Didemnum cilicium Kott 2005a, p 2438 .

Distribution

Previously recorded (see Kott 2005a): South Australia (Kangaroo I.); Tasmania (Triabunna); Victoria (Bass Strait, Western Port , Cape Woolamai) ; New South Wales (Port Jackson,? Jervis Bay ). New record : Queensland ( Noosa , QM G308767 ) .

Description

In preservative, the newly recorded colony is a fleshy grey sheet, although in life it has yellow-pinkish patches in the surface, and black borders around the common cloacal apertures. There is a relatively thick superficial layer of bladder cells. In preservative, the surface is marked with a network of grey where it is depressed over the circular primary common cloacal canals. The grey over the common cloacal canals results from the interruption of the spicule-containing test by the deep canals. In the zooid-containing elevated areas surrounded by the canals, the greater depth of spicule-containing test creates whiter, opaque areas. Spicules, crowded throughout the test, are stellate, to 0.075 mm diameter, with 9–11 (and occasionally more) robust, conical, pointed rays in optical transverse section. The common cloacal canals are deep, sometimes the whole depth of the zooids, but are never posterior abdominal.

Zooids have a long thorax, wide open, sessile, atrial aperture without an anterior lip, long lateral organs, a fine long retractor from halfway down the oesophageal neck, and a double gut loop. Gonads were not detected in this specimen.

Remarks

Moderate-sized stellate spicules with robust conical rays occur in Didemnum lissoclinum and D. crescente , which also have deep primary common cloacal canals around clumps of zooids, but in which the number of spicule rays is less than in the present species. Although D. crescente also has a superficial bladder cell layer it is not as conspicuous as in the present species.

Didemnum fragum has similar spicules but it also has a thin superficial layer of bladder cells rather than the conspicuous one of the present species, and its colonies are large vertical cones with terminal common cloacal apertures and extensive three-dimensional common cloacal systems rather than sheet-like colonies.

Didemnum plebium Kott, 2005a from tropical northwestern Australia has similar but smaller spicules and small colonies.

Didemnum cilicium Kott, 2005a appears to be a junior synonym of the present species.

Didemnum patulum: Kott, 2005a is a specimen from Jervis Bay that may be assigned incorrectly. It has a fleshy colony and, although the spicules are a similar shape, they are smaller and less crowded than the present ones, becoming sparse in the basal test. They have 9–11 rays in optical transverse section but the conical rays have pointed or chisel-shaped tips and the spicules (to 0.05 mm diameter) are smaller than those of D. patulum .

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).