Polysyncraton discoides Kott, 1962

Kott, Patricia, 2005, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (Part 3), Journal of Natural History 39 (26), pp. 2409-2479 : 2429

Polysyncraton discoides Kott, 1962

Polysyncraton discoides Kott 1962, p 303 (part, syntypes from Rottnest I.); 2001, p 98 and synonymy.

Distribution

Previously recorded (see Kott 2001): Western Australia (Rottnest I.); Tasmania (Port Davey). New record: South Australia (Great Australian Bight, Fowler’s Bay jetty piles, SAM E2642 ) .

Description

The colony is a small (2 cm maximum diameter), relatively soft cushion with spicules crowded throughout, absent only from a superficial layer of bladder cells through which the short branchial siphons project, the branchial apertures being conspicuous on the surface of the colony. A large sessile common cloacal aperture with a spicule-free rim is in the centre of the upper surface. The common cloacal cavity is thoracic. Spicules are relatively small (to 0.046 mm), globular burr-shaped with numerous crowded rod-like rays. Small pointed branchial lobes are on the rim of the branchial apertures, the atrial aperture has a biramous anterior lip and there is a retractor muscle projecting from halfway down the short oesophageal neck. Gonads were not detected.

Remarks

The newly recorded specimen confirms the southern Australian range for this species, which previously was known only from two widely separated records. Although the largest spicules have a slightly greater diameter than has previously been recorded for the species, they are the same burr-like globular shape and the small cushion-like colonies with a central common cloacal cavity are similar to those of the syntypes from Rottnest I.