Didemnum ossium 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 : 756

Didemnum ossium Kott, 2001

Didemnum ossium Kott, 2001: 216 and synonymy.

Distribution. New record: NW Australia (Passage Is, WAM 160.93). Previously recorded (see Kott, 2001): NW Australia (Lord Mayor Shoal, Montebello Is, Bonaparte Archipelago), Northern Territory, New Caledonia, Philippines.

Description. The colony has cylindrical to tongue-shaped lobes that branch and fuse along their length. Conspicuous, white-rimmed, sessile common cloacal apertures are randomly placed on the surface. Spicules are crowded in a layer at the surface and they form a rod in the centre of the central test core. They are not present elsewhere. The posterior abdominal common cloacal cavity surrounds the central test core and is continuous with the primary canals that surround clumps of zooids. Secondary cavities penetrate in amongst the thoraces in each clump, separating them from one another. Embryos are in the central test around the outside of the central rod of crowded spicules. Larvae are of the usual form with a ring of about 34 narrow epidermal ampullae around the three antero-median adhesive organs. They were collected in December.

Zooids have a retractor muscle and nine coils of the vas deferens. Spicules (to 0.06 mm diameter) have 9–11 pointed conical or blunt-tipped rays in optical transverse section. Sometimes the rays have bifid tips.

Remarks. The absence of spicules from part of the colony has not previously been reported for this species, although spicules are reported to be more crowded in the central axis than elsewhere (see Kott, 2001).