Didemnum microthoracicum 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 : 1185-1186

? Didemnum microthoracicum Kott, 2001

( Figures 3B , 9B )

Didemnum microthoracicum Kott 2001, p 207 ; 2005a, p 2448.

Distribution

Previously recorded (see Kott 2005a): South Australia (Great Australian Bight, Kangaroo I.). New record: South Australia (Kangaroo I., SAM E3259 ) .

Description

The colony is a robust encrusting sheet, white in preservative. In life, brown pigment, in irregular granular bodies, is over the common cloacal canals that converge to large protuberant common cloacal apertures, the brown pigment forming evenly spaced dendritic bodies with about five long, tapering, radial arms. Branchial apertures are stellate with their margins lined with spicules. Spicules are moderately crowded throughout the test and the surface is raspy. Up to eight radial ribs of crowded spicules strengthen the roof of the common cloacal cavity around the common cloacal apertures. The spicules are stellate, to 0.086 mm diameter, with seven to nine robust, pointed, conical rays in optical transverse section. The common cloacal cavity is thoracic, with deeper primary canals. Thoraces have up to seven stigmata per half row. Gonads were not detected.

Remarks

The form of the spicules and their size and distribution are the same as those in previously recorded specimens of this species. All known specimens are from South Australian waters, and it has been recorded previously from Kangaroo I. The latter specimen was blue in life, while the newly recorded one has brown pigment over the common cloacal canals where they converge to the common cloacal apertures. For this reason the present assignation is uncertain.

Didemnum corium Kott, 2005a (from Tasmania) has similar spicules, although their distribution is different from the present species.

Figures

Figure 3. (A) Didemnum mantile (QM G308887): larva. (B) Didemnum microthoracium (SAM E3259): colony. (C, D) Didemnum parau (QM G308859): (C) abdomen; (D) larva. Scale bars: 0.1 mm (A, C, D), 5 mm (B).

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).