Polysyncraton reticulum Kott, 2004

Kott, Patricia, 2007, New and little-known species of Didemnidae (Ascidiacea, Tunicata) from Australia (part 4), Journal of Natural History 41 (17 - 20), pp. 1163-1211 : 1173-1174

Polysyncraton reticulum Kott, 2004

( Figures 1G , 7D )

Polysyncraton reticulum Kott 2004b, p 2484 .

Distribution

Previously recorded (see Kott 2004b): South Australia (Kangaroo I.). New records: Tasmanian Canyons (King I. Canyon, 195.8 m, QM G323330 ) .

Description

The newly recorded colony is a small, hard, white strip encrusting a calcareous worm tube. Spicules are crowded in the surface and basal test, but are sparse elsewhere. They are burrlike to globular, to 0.06 mm in diameter with 15–19 long, crowded, rod-like, fusiform or flat, pointed- and irregular-tipped rays in optical transverse section. A roomy common cloacal cavity is at thorax level. The zooids are muscular and very contracted and most details of their structure are obscured. A wide transverse atrial opening has an anterior lip. The stigmata are in four rows with 10 per half row. A very short retractor muscle (contracted) projects from the top of the oesophageal neck. A large egg projects from the side of the long gut loop in some of the zooids. Testes are not present. Large larvae in the basal aspiculate layer of test have a trunk 1.0 mm long. At the anterior end of the trunk, a corona of 16 L-shaped lateral ampullae surrounds the three anteromedian adhesive organs that each has a long, straight, parallel, thick cylindrical stalk and a deep epidermal cup surrounding the relatively narrow cone of adhesive cells that is more or less the same diameter as the stalk. The lateral ampullae project out around the base of the stalks of the adhesive organs and then bend forwards at right angles to the longitudinal axis of the trunk. Four rows of small circular stigmata are in the larval pharynx, and an ocellus and otolith are present. The tail is relatively short and curves about halfway around the trunk. The oozooid is relatively rudimentary and blastozooids were not detected.

Remarks

Despite the poor condition of this specimen and the lack of information about the zooids, the large larvae with long, thick parallel stalks supporting the deep narrow, epidermal cups that surround the narrow adhesive cones of the adhesive organs and the numerous lateral ampullae bent at right angles to encircle the anterior end to the trunk are similar in many other Polysyncraton spp. Also, the rudimentary condition of the organs of the oozooid (e.g. the pharynx) is consistent with Polysyncraton spp. The larvae of the present species, previously not known, resemble those of P. circulum Kott, 1962 , which has more spicule rays and is tropical. Known species of Polysyncraton spp. with about 20 crowded spicule rays in optical transverse section with a range of flat to pointed ray-tips are P. rugosum Monniot, 1993 , P. discoides Kott, 1962 , and P. dromide Kott, 2001 . Their spicules are smaller than those of the present species and only P. discoides is known from temperate waters (Port Davey). Polysyncraton dentatum Kott, 2001 has spicules to 0.04 mm diameter with more compact rays than the present species, and P. pulchrum Kott, 2001 has spicules to 0.05 mm diameter with more needle-like rays. The latter species, known only from Western Australia, has a unique soft, vase-like colony. Although the present specimen has a range of 15–19 spicule rays in optical transverse section, Kott (2004b) recorded a range of 13–15. In view of the variations in the number of rays in these burr-like spicules with large number of rays and the difficulty of counting them, this difference is not significant and the specimens appear to be conspecific. The assignation of this newly recorded species is based on the similar zooids and the size, form and distribution of its spicules.

Figures

Figure 1. (A) Atriolum irregulare (QM G323245 holotype): larva. (B, C) Leptoclinides fluxus (QM G308817 holotype): (B) colony surface; (C) zooid. (D–F) Polysyncraton gratum (QM G308891): (D) thorax; (E) abdomen; (F) larva. (G) Polysyncraton reticulum (QM G323330): larva. Scale bars: 0.1 mm (A, C–G); 1 mm (B).

Figure 7. Scanning electron micrographs. (A) Polysyncraton magnetae (QM G308818); (B) Polysyncraton meandratum (QM G308849); (C) Polysyncraton otuetue (QM G308851); (D) Polysyncraton reticulum (QM G323330); (E) Polysyncraton scorteum (QM G323343); (F) Didemnum abradatum (QM G308870); (G) Didemnum astrum (QM G308857); (H) Didemnum candidum (QM G308765).