Polysyncraton miniastrum, 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 : 743

Polysyncraton miniastrum sp. nov.

( figure 6B, C )

Distribution. Type locality: Queensland (Shelburne Bay, 22 m, encrusting worm tube, coll. AIMS Bioactivity Group, 11 April 1994, holotype QM G308537).

Description. The colony is a smooth-surfaced encrusting sheet. Spicules are in a thin layer in the surface and the base, but are only patchy or sparse between. Those in the surface layer are interrupted by evenly spaced stellate branchial apertures and minute spherical vesicles are arranged in a circle around each branchial aperture. Spicules are small (to 0.036 mm diameter) with 17–19 relatively short conical rays in optical transverse section. The common cloacal cavity is thoracic. The colony is said to have been orange in life.

Contracted zooids in the holotype have large thoraces with short cylindrical branchial siphons and large sessile atrial apertures with a pronounced tongue from the anterior rim of the opening. The number of stigmata could not be accurately determined but there appear to be more than 10 per row in the wide thorax. A retractor muscle was not detected, but may be present. The gut loop is long and the testis, against the dorsal side of the distal end of the loop, has four or five testis follicles and is surrounded by four well-separated coils of the vas deferens. Larvae are not known.

Remarks. The only other Polysyncraton known to have similar small spicules is Polysyncraton magnetae Hastings, 1931 which, however, has a diversity of spicule shapes, some stellate with long pointed rays and others almost globular with rounded or flat-tipped rod-like rays. Further, P. magnetae has a thin superficial layer of bladder cells, its spicules are crowded throughout and its zooids are arranged along each side of circular canals.

Polysyncraton circulum Kott, 1962 is a tropical species with similar vesicles surrounding each branchial aperture and spicules missing from the centre of the colony. However, spicules are larger with more rays and some are globular and sometimes hollow.

Figures

FIG. 6. Polysyncraton millepore (WAM 207.93): (A) colony. Polysyncraton miniastrum (QM G308537): (B) zooid; (C) spicules. Scales: (A) 1.0 cm; (B) 0.1 mm.