Didemnum patulum ( Herdman, 1899 )

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 : 756-757

Didemnum patulum ( Herdman, 1899)

Leptoclinum patulum Herdman, 1899: 92 .

Didemnum patulum: Kott, 2001: 219 and synonymy.

Distribution. New records: Tasmania (Triabunna jetty piles, SAM E2903); Victoria (Western Port, MV F70225 ; Portsea Pier, SAM E2913–4 E3202). New South Wales (Port Jackson, AM Y2338). Previously recorded (see Kott, 2001): Victoria (Cape Woolamai, Western Port, Gabo I., Bass Strait), New South Wales (Port Jackson).

Description. Preserved colonies are encrusting sheets with their surface marked with a network of depressions over the primary canals, which surround clumps of zooids. Shallow secondary common cloacal cavities penetrate amongst the zooids at thorax level. Surface and basal layers of test forming the roof and floor of these canals is very thin. The branchial openings are lined with spicules. Spicules are crowded throughout the colonies. They are to 0.07 mm diameter with 9–11 robust, pointed conical rays in optical transverse section. Zooids are small, with a long, narrow retractor muscle from the middle of the oesophageal neck. Six stigmata are in the anterior row in the branchial sac. The lateral organ is a scoop-shaped projection each side of the endostyle with the cavity facing postero-ventrally. The vas deferens coils eight times around a large, spherical, undivided testis (SAM E2903, MV F70225 ).

Remarks. Most characters are as described for this species. Previously unconfirmed, Kott’s (1962) count of eight coils of the vas deferens in specimens from Balnarring Beach is confirmed in the newly recorded material. The newly recorded colony from Port Jackson was found as an epibiont on a specimen of Microcosmus squamiger Hartmeyer and Michaelsen, 1928 (family Pyuridae ).

So far this species is known only from a limited geographic range around the south-eastern corner of the continent, where it often is encountered.