Polysyncraton longitubis, 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 : 2480-2481

Polysyncraton longitubis sp. nov.

( figures 5A , 17B )

Distribution. Type locality: South Australia (Kangaroo I., between Western River Cave and Snug Cove, The Arch on rock wall, 10–14 m, coll. K. Gowlett Holmes, 28 November 2001, holotype SAM E2929).

Description. The colony is a hard, black plate with a rounded margin, more or less circular and about 8 cm diameter. The black pigment is in spindly stellate bodies that may be chromatophores. These form a black layer on the surface

where they are mixed with spicules. The pigmented bodies continue down into the siphon lining and also form a layer on the base of the colony. Pigment bodies are also scattered in the remainder of the colony which is white and opaque with crowded spicules. Zooids open along each side of the surface depressions over the deep primary common cloacal canals that surround the solid pillars of test in which the ventrum of each zooid is embedded, and that form rounded swellings of the colony surface. A few spicules are in the branchial siphonal linings but do not outline the apertures. Common cloacal apertures are randomly spaced on the surface. Spicules are small, to 0.04 mm diameter, and of two types: some stellate with 9–11 conical rays in optical transverse section and others with a similar number of truncated flat-tipped rays that form almost globular spicules.

Zooids have a large tulip-shaped branchial siphon, a large sessile atrial opening with an anterior tongue (small and simple to larger, flattened with a concave tip), a large branchial sac with nine stigmata in the anterior row, eight in each of the next two rows and seven in the last row, a strong retractor muscle projecting from halfway down the oesophageal neck, a double gut loop, and 10 vas deferens coils around four or five testis follicles. In some of the zooids from the holotype colony, the coils of the vas deferens appear to have slipped back from the testis to enclose part of the gut loop in the spiral. This is probably an artefact.

Remarks. The colony form and pigmentation closely resemble the tropical species P. millepore Vasseur, 1969 (see Kott, 2001), which has similar spicules, some almost globular with truncated rays and others stellate with conical rays. The present species has fewer rays and 10 (rather than five) coils of the vas deferens.

The large number of vas deferens coils is an unusual character in zooids of this genus.

Figures

FIG. 5. (A–C) Polysyncraton longitubis (SAM E2929). (A) Surface of colony; (B) thorax; (C) abdomen. (D, E) Polysyncraton montanum (SAM E3224). (D) Thorax; (E) abdomen. Scale bars: 5.0 mm (A, C); 0.1 mm (B, D, E).

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).