Polysyncraton rostrum, 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 : 2486-2487

Polysyncraton rostrum sp. nov.

( figure 18A )

Distribution. Type locality: Northern Territory (South Shell I., 7–11 m, coll. B. Glasby and party, holotype QM G308631; paratype QM G308628).

Description. The colonies are encrusting sheets, the holotype pinkish white with some orange flecks in life and the paratype is more yellowish beige overall with extensive orange patches. Both are white in preservative. Opaque white circles are around the common cloacal apertures. The lobes of the evenly distributed branchial apertures protrude from the surface like small daisies. A pointed, spicule-filled papillum projects from the surface at the base of each of the branchial lobes in the paratype, although actual papillae are not present in the holotype. The surface of the colony is raspy and hard with crowded spicules. Generally, the spicules are crowded throughout, although sometimes they are less crowded in the middle of the basal layer of test. Spicules are large (to 0.1 mm diameter) and stellate with seven to nine sharply pointed conical rays in optical transverse section. The common cloacal cavity is thoracic and abdomina are crowded in the upper part of the basal layer of test. Terminal ampullae of the stolonic vessels are conspicuous in the basal layer of test.

Zooids have a bifid atrial tongue and a retractor muscle projects from the top of the oesophageal neck. Three coils of the vas deferens surround about eight testis follicles.

Remarks. The size of the relatively large spicules with relatively few and sharply pointed rays are characteristic of this species. The spicules of Polysyncraton sideris Kott, 2001 are similar but have a greater maximum diameter, and more coils of the vas deferens than the present species; and the spicules of P. cuculliferum are significantly smaller with more rays.

Polysyncraton tegetum Kott, 2001

( figures 6B , 18B )

Polysyncraton tegetum Kott, 2001: 137 and synonymy.

Distribution. Previously recorded (see Kott, 2001): South Australia (Great Australian Bight). New record: South Australia (Kangaroo I., SAM E3213).

Description. The newly recorded colony is sheet-like with a smooth surface, slightly blotchy reddish tan in life and orange in preservative. Zooids are orange. Spicules are not particularly crowded. They are scattered in the superficial layer of test where they are mixed with pigment cells. They are present also through the zooid layer but are absent from the basal quarter of the colony, where the test is transparent. The colony is very tough and the zooids are impossible to remove from it. Neither common cloacal apertures nor common cloacal cavity were detected in the newly recorded specimen. The spicules (to 0.075 mm diameter) are stellate, with chisel-tipped or conical pointed rays. Some of the smaller spicules have as few as seven rays in optical transverse section but some of the larger ones have as many as 13, often chisel-tipped rays.

Zooids have a moderately long, cylindrical branchial siphon. The atrial aperture is a wide opening with a broad flat-tipped anterior lip. A fine retractor muscle projects from halfway down the oesophageal neck. About eight stigmata are in the anterior row but these could not be counted accurately. The gut forms a simple vertical loop, the pole of the loop flexed ventrally only when gonads mature. Buds are attached to the oesophageal neck by relatively long stolons. Mature testis follicles (about five) with seven coils of the vas deferens were detected in only one of the zooids examined. A large egg often is present at the posterior end of the abdomen of the newly recorded specimen, some embryos are being incubated in the basal test, and a few larvae are being liberated through the colony surface. Larvae are robust, almost spherical with the tail wound the whole way around the 0.5 mm-long trunk. Four lateral ampullae are along each side of the three antero-median adhesive organs and an external ampulla projects almost vertically from the neck behind the adhesive array on the left side. Four rows of stigmata are in the larval pharynx.

Remarks. The large zooids of the newly recorded colony with their broad flat-tipped atrial tongues are identical with those figured by Kott (2001: figure 68B, C) for this species. The chisel-shaped tips of the spicule rays resemble those found in many species of Leptoclinides but are not known in other species of Polysyncraton , although the large zooids, vertical gut loops and four rows of stigmata in the larval pharynx are characteristic of the genus.

As with some other specimens from Kangaroo I. in this collection ( Leptoclinides comitus , L. variegatus ), the maximum-sized spicule is only half the diameter of that previously recorded for the species.

Figures

FIG. 18. (A) Polysyncraton rostrum (QM G398628); (B) Polysyncraton tegetum (SAM E3213); (C) Polysyncraton textus (WAM 556.88); (D) Didemnum albopunctatum (QM G308627); (E) Didemnum candidum (WAM 557.88); (F) Didemnum congregatum (WAM 192.90); (G) Didemnum coralliforme (QM G308629); (H) Didemnum crescente (SAM E3208).

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.