Didemnum coralliforme, 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 : 748-749

Didemnum coralliforme sp. nov.

( figure 9 )

Distribution. Type locality: Western Australia (W of Port Hedland, CSIRO Stn 126, 50 m, 30 August 1983, holotype NTM E34).

Description. The colony is opaque, a milky-pink colour, crowded with spicules, and irregularly encrusting weed, with some branches and lamellae projecting from the surface. Spicules are packed especially hard in the basal test, and in the test core of branches (where they form a central axis providing a frame or internal skeleton for the colony). Stellate branchial apertures, with their margins outlined by spicules, are evenly spaced on the hard, flat surface.

Double circles of large spherical vesicles interrupt the spicules around each branchial aperture. Spicules are stellate, to 0.085 mm diameter, with seven to nine long conical rays in optical transverse section, the ray length / spicule diameter ratio being 0.37. Comma-shaped thoraces cross the thoracic common cloacal cavity with a ventral sheath of test. Abdomina are embedded in the basal test.

Zooids are robust with a well-defined, tulip-shaped branchial siphon, a short retractor muscle from halfway down the oesophageal neck, the post-pyloric part of the gut loop bent ventrally at right angles to the long axis of the zooid, and eight coils of the vas deferens around an undivided testis. Larvae are not known.

Remarks. Spicules are like those of D. madeleinae Monniot and Monniot, 2001 and D. perplexum Kott, 2001 , but are larger and have a few more and longer spicule rays. Didemnum grande has similar spicules but only seven coils of the vas deferens and D. granulatum has similar but smaller spicules and only six coils of the vas deferens. Didemnum captivum Monniot and Monniot, 1997 from Tanzania has eight vas deferens coils and similar but smaller spicules (0.04 mm diameter).

The vesicles in the surface test which interrupt the spicules around each branchial aperture have formerly been reported for D. spadix Kott, 2001 , although they are known also in Polysyncraton ( P. circulum , P. miniastrum and P. orbiculum ).

Figures

FIG. 9. Didemnum coralliforme (NTM E34): (A) colony with branches sectioned to show central test core; (B) thorax; (C) abdomen from right side; (D) abdomen, ventral view; (E) spicules. Scales: (A) 1.0 mm; (B–D) 0.1 mm.