Polysyncraton turris, 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 : 746-747

Polysyncraton turris sp. nov.

( figure 8 A–C)

Distribution. Type locality: Queensland (Shelburne Bay, 43 m, coll. AIMS Bioactivity Group, 22 March 1994, holotype QM G308538).

Description. The rather gelatinous colony is sheet-like and encrusting. A thin superficial layer of bladder cells overlies a relatively sparse layer of spicules at zooid level. Beneath the zooids, the basal test is translucent and spicule-free. The cloacal cavity is thoracic but limited and inconspicuous. Spicules are stellate, to 0.07 mm diameter with 13–15 long, spiky, pointed rays, occasionally truncated (or broken off?) at the tip or near the base of the ray. The ray length / spicule diameter ratio is about 0.35 or more. A group of two or three spicules is in the branchial siphon lining. The colony is said to have been light pink in life.

Zooids are about 1.5 mm long, a long branchial siphon is about one-third of the length of the rest of the thorax and has six shallow lobes around the aperture. The large atrial aperture exposes most of the branchial sac, and has a forked atrial tongue from its anterior margin. An oval lateral organ is opposite the first interspace between the rows of stigmata. A fine retractor muscle projects from the top of the relatively long oesophageal neck. About nine stigmata are in the anterior row, reducing to six in the posterior row. The gut forms a relatively short loop with gonads against its dorsal side. In some zooids, four coils of the vas deferens surround four or five testis follicles. In others, the testis appears to be degenerate and spermfilled coils of the vas deferens (acting as a seminal vesicle) lie against a large egg in the abdomen. Larvae are not known.

Remarks. Zooids of the known specimens of Polysyncraton arafurensis Tokioka, 1952 are similar to the present species, spicules are similar (with 13–15 pointed rays) and type localities are not far removed from one another. However, the spicule rays of the present species are longer and more attenuated than those of P. arafurensis and the rather gelatinous colony with its spicule-free base and superficial bladder cell layer also differs from the hard spicule-filled colonies of P. arafurensis . The present species also lacks the marginal spicules outlining the stellate branchial apertures on the surface of P. arafurensis colonies. Polysyncraton millepore Vasseur, 1969 has similar attenuated spicule rays to the present species but they are fewer and colonies are thin, hard and packed with spicules throughout.

The attenuated spicule rays and gelatinous colony with spicules missing from the surface and the basal half of the colony are characteristic of this species.

Figures

FIG. 8. Polysyncraton turris (QM G308538): (A) thorax; (B) abdomen; (C) spicules. Didemnum asterix (WAM 633.88): (D) spicules. Scales: (A, B) 0.1 mm.