Polysyncraton peristroma, Kott, 2010

Kott, Patricia, 2010, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (part 2), Journal of Natural History 38 (26), pp. 2455-2526 : 2482-2483

Polysyncraton peristroma sp. nov.

( figure 17D )

Distribution. Type locality: Northern Territory (Darwin, Angler Reef, 10–12 m, coll. B. Glasby and party, 31 August 2002, holotype QM G308608).

Description. In life the surface of the encrusting colony has a conspicuous black network resulting from pigment in the surface test over the common cloacal canals which surround cream/yellow flat-topped stands of solid test, their smooth flat tops looking like scales on the surface of the colony. The common cloacal canals are lined on each side by the zooids, which have their ventral surfaces embedded in the test and their abdomina curved dorsally in the test lining the bottom of the cloacal canals. The layer of test lining the common cloacal canals where zooids are embedded is spicule-free but the remainder of the test is packed hard with spicules. Spicules are stellate, to 0.06 mm diameter with seven to nine long, conical, but often almost rod-like, rays in optical transverse section.

Zooids have a short branchial siphon. The atrial aperture is wide, its anterior rim projecting from the zooid in a wide arc, but an atrial lip is not formed. The thorax is long, comma-shaped, the oesophageal neck is long with a retractor muscle projecting from near its base and the remainder of the abdomen also is long. Five or six coils of sperm-filled vas deferens surround six or seven male follicles and there is a large yellow egg. The sperm-filled coils of the vas deferens often persist as a seminal vesicle after degeneration of the testis follicles.

Remarks. Many species of this genus have similar common cloacal canals lined on each side with zooids and surrounding zooid-free stands of test. Only P. catillum has similar spicules with long, almost rod-like spicule rays, although they are smaller, and the rays are more numerous than in the present species.

Figures

FIG. 17. (A) Polysyncraton galaxum (SAM E2927); (B) Polysyncraton longitubis (SAM E2929); (C) Polysyncraton montanum (SAM E3224); (D) Polysyncraton peristroma (QM G308608); (E) Polysyncraton pseudomagnetae (QM G308612); (F) Polysyncraton pseudorugosum (QM G308600); (G) Polysyncraton reticulum (SAM E2917); (H) Polysyncraton rica (SAM E3216).