Didemnum diversum, Kott, 2004

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 : 749-750

Didemnum diversum sp. nov.

( figure 10 )

Distribution. Type locality: Western Australia (Passage Is, NW Long I., 16– 15 m, coll. S. Slack-Smith and L. Marsh on RV Soela, 10 December 1979, holotype WAM159.93). Description. In preservative the colony is a smooth flesh-coloured sheet. The preserved zooids especially the anterior end of the endostyle are pink, and this, seen through the relatively sparse spicules, confers the flesh colour to the colony. Spicules are present throughout but they are crowded only in the basal test, which has ripple marks. Elsewhere, especially in the lower half of the colony, the test is relatively fleshy. Primary common cloacal canals around groups of zooids are deep and sometimes become posterior-abdominal. Secondary common cloacal cavities surround the zooids at thorax level. Spicules, to 0.05 mm diameter, are diverse, some stellate with pointed conical or truncated rays, the latter varying in length, sometimes being so short that the spicules are almost globular. The tips of the conical rays often are divided and a few have a saw-tooth or pectinate appearance. Rays are 13–15 in optical transverse section.

Zooids are small with a short branchial siphon, a wide open, sessile atrial opening without an atrial lip, nine fusiform stigmata in the anterior row, a retractor muscle from halfway down the long oesophageal neck and eight coils of the vas deferens around an undivided testis. Larvae are not known.

Remarks. Of the species with a similar diversity of spicules (albeit lacking the saw-tooth-edged rays of some in the present species), Didemnum bisectatum Kott, 2001 , D. chartaceum Sluiter, 1909 and D. multispirale Kott, 2001 have larger spicules with more rays, D. elongatum Sluiter, 1909 and D. moseleyi ( Herdman, 1886) fewer spicule rays (to 11 in optical transverse section), D. inveteratum Kott, 2001 has much larger spicules and other characters of zooids and colonies that distinguish them from the present species; and although D. ossium Kott, 2001 has spicules that resemble the present species in both size and form, its zooids and colony are different.

Spicules with irregular and sometimes subdivided and pectinate ray tips have been reported for Trididemnum cristatum Kott, 2001 and Didemnum cygnuus Kott, 2001 , but in both of these species the spicules have fewer rays than the present species and are absent from much of the colony.

Figures

FIG. 10. Didemnum diversum (WAM 159.93): (A) thorax; (B) abdomen; (C) spicules. Scales: (A, B) 0.1 mm.