Polysyncraton luteum, 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 : 739-740

Polysyncraton luteum sp. nov.

( figure 5 )

Distribution. Type locality: Victoria (Flinders Pier, 4–6 m, coll. J. Watson, September 2000, holotype QM G308565).

Description. The colony is a hard, flat, irregular sheet, orange in life. Zooids are in clumps surrounded by deep circular canals. Spicules are crowded throughout the test. Small (orange in life) spherical vesicles are scattered in the surface test amongst the spicules. Spicules are small, to 0.025 mm diameter, globular with 11–13 thick round-tipped rays, or stellate with a short conical point in the centre of the circular terminal surface of each ray.

Zooids are about 1.0 mm long overall. They have a robust cylindrical branchial siphon with six pointed lobes around the aperture. A pronounced bifid lip projects from the anterior rim of the atrial opening. An oval lateral organ is on each side of the thorax. About eight stigmata are in the anterior row of the branchial sac, but the exact number is obscured by contraction. A robust retractor muscle projects from the oesophageal neck. The vas deferens coils eight times around four or five testis follicles. Embryos are being incubated in the basal test. The large larval trunk (1.0 mm long) has the tail wound three-quarters of the way around it. Three anteromedian adhesive organs are surrounded by a circle of 30 ectodermal ampullae. An otolith and ocellus are present, and the outer surface of the larval test is ornamented with fine striations. Other organs were not detected although the size of the trunk suggests that blastozooids could be present.

Remarks. Both zooids and larvae are characteristic of Polysyncraton , although there are more vas deferens coils than in most species of that genus. The large vesicles scattered in the surface test are similar to those in P. orbiculum Kott, 1962 and P. circulum Kott, 1962 . However, both have larger spicules than the present species, and their vesicles are more regularly arranged. The spicules in the present species are similar to those of the tropical P. magnetae Hastings, 1931 (with a similar colony but only three coils of the vas deferens) and P. miniastrum (with similar spicules but with fewer rays and lacking spicules in the middle layer of the colony, see below).

Figures

FIG. 5. Polysyncraton luteum (QM G308565): (A) thorax; (B) abdomen; (C) larva; (D) spicules. Scales (A–C) 0.1 mm.