Polysyncraton reticulum, 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 : 2484-2486

Polysyncraton reticulum sp. nov.

( figures 6A , 17G )

Distribution. Type locality: South Australia (Kangaroo I. between Snug Cove and Western River, The Cave on rock wall, 10–12 m, coll. K. Gowlett Holmes, 12 December 1999, holotype SAM E2917).

Description. The holotype is a soft, thin encrusting sheet. The thin superficial layer of test has a few sparse spicules scattered in it and a few spicules are in the branchial siphon linings, but they do not outline the apertures. Beneath the superficial layer of test the spicules are crowded around, but not over, the pink zooids so that, when seen from the surface, the colony appears to have a white net or a pinkish white cloth over the surface, enclosing pink spots in its meshes. In life the spots where the zooids open are dark pink. Numerous randomly distributed sessile common cloacal openings are each surrounded by a circle of spicule-free test through which the spicules can be seen, crowded in the floor of the shallow common cloacal cavity. Spicules are burr-like with 13–15 club- to rod-shaped rays in optical section and are to 0.06 mm in diameter. Zooids are evenly distributed, the thoraces crossing the common cloacal cavity with a short ventral strip of spicule-filled test. Deeper primary canals were not detected. Abdomina are embedded in the relatively thick basal test.

Zooids have the tips of the branchial lobes and anterior part of the thorax covered with conspicuous projecting columnar epithelial cells. A long retractor muscle projects from about halfway down a relatively short oesophageal neck and a bifid, forked atrial tongue projects from the upper rim of the opening. Three coils of the vas deferens surround five to seven testis follicles.

Remarks. The spicules of the present species resemble those of the majority of Polysyncraton species. In particular, they are like the temperate species P. discoides Kott, 1962 , having about the same number of similar spicule rays and the same number of male follicles and vas deferens coils. However, the spicules of P. discoides are smaller than those of the present species, they line the margins of the branchial apertures and, unlike the present species, deep primary common cloacal canals extend the full depth of the zooids and interrupt the even horizontal common cloacal chambers and the even distribution of the zooids.

Polysyncraton rica Kott, 2001

( figure 17H )

Polysyncraton rica Kott, 2001: 130 ; 2004 and synonymy.

Distribution. Previously recorded (see Kott, 2001, 2004): South Australia (Great Australian Bight; Spencer Gulf, Gulf St Vincent, Kangaroo I.). New records: South Australia (Kangaroo I., SAM E3216; Flinders I., QM G2387).

Description. In preservative, colonies are pinkish cream slabs up to 1.0 cm deep in the centre where the basal layer of test is particularly thick. Branchial apertures are depressed into the surface, sometimes visible along each side of deep (but not posterior abdominal) primary common cloacal canals around circular to longish oval stands of test. Zooids are orange. A conspicuous superficial, aspiculate, bladder cell layer is on the surface of the colony. Spicules are stellate but some are irregular or bilaterally symmetrical. They have 11–13 strongly conical pointed rays in optical transverse section. Some are large, to 0.075 mm diameter, but other small stellate spicules are mixed with them. They are slightly more crowded in the surface and basal layers of test are elsewhere. A few, large common cloacal apertures with aspiculate rims are near the outer margins of the colony and are protected by the bladder cell layer when the colony is contracted. Zooids are almost vertical in the colony. They have moderately long cylindrical branchial siphons and atrial lips and a long retractor muscle. Large larvae are in the basal test of specimens collected in March (SAM E3216).

Remarks. The spicules resemble those of P. galaxum , being a mixture of large and very small ones. Generally, they are larger than those of P. galaxum and have more rays. Spicules of P. pseudorugosum are a similar size but have fewer rays.

Figures

FIG. 6. (A, B) Polysyncraton reticulum (SAM E2917). (A) Thorax; (B) abdomen. (C, D) Polysyncraton tegetum (SAM E3213). (C) Thorax; (D) larva. Scale bars: 0.1 mm.

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).