Polysyncraton textus, 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 : 2487-2489

Polysyncraton textus sp. nov.

( figure 18C )

Distribution. Type locality: Western Australia (8.5 n. mls NW of Port Hedland, 18 m, coll. J. Fromont on RV Soela, 5 August 1982, holotype WAM 556.88).

Description. The colony is an extensive white sheet overgrowing worm tubes. It is white in preservative. Stellate branchial apertures with a margin of spicules are arranged around small intensely white unperforated areas of the surface. Deep primary common cloacal canals extend the full length of the zooids and surround circles of zooids with their ventral surfaces embedded in ligaments of test between the surface and base of the colony. Small spicule-filled papillae are crowded on the surface between the branchial apertures. An even layer of relatively crowded spicules is in the surface test and another less crowded layer is on the base of the colony. Spicules are sparse elsewhere. The spicules are small, stellate, to 0.037 mm diameter, with 15–17 relatively short and irregular, sometimes subdivided conical rays in optical transverse section. The ray length/spicule diameter ratio is about 0.2.

Zooids have a tulip-shaped branchial siphon and a large bifid atrial tongue. The branchial sac is large, but the stigmata could not be counted. Three coils of the vas deferens surround four or five testis follicles, the outside coil encircling the base of a large egg. Larvae being incubated in the basal test have a trunk 0.85 mm long with the tail wound about three-quarters of the way around it. A corona of about 16 round-tipped lateral ampullae surround the three anteromedian ampullae at the anterior end of the trunk. The larval pharynx does not appear to be perforated, although the gut is differentiated and the otolith and ocellus are present. Blastozooids were not detected.

Remarks. Relatively few species in this genus have stellate spicules similar to the present ones. Polysyncraton arafurensis Tokioka, 1952 and P. multiforme Kott, 2001 do have similar spicules although they are larger than those of the present species and are crowded throughout the colony. Other characters, such as the large bifid atrial tongue, the large larvae with relatively rudimentary larval organs but large number of lateral ampullae and the loose and relatively few coils of the vas deferens are characteristic of many Polysyncraton spp.

Didemnum albopunctatum Sluiter, 1909

( figure 18D )

Didemnum albopunctatum Sluiter, 1909: 58 ; Kott, 2001: 148 and synonymy; 2004.

Distribution. Previously recorded (see Kott, 2001, 2004): Western Australia (Rowley Shoals), Queensland (Capricorn Group, Swain Reefs, Whitsunday Is), Indonesia, New Caledonia, Palau Is, Fiji. New record: Northern Territory (Dudley Bommies, QM G308627).

Description. The newly recorded colony is soft and flexible, possibly due to the small spicules and the deep common cloacal cavity. They are whitish black in life with white rims around the common cloacal apertures. In preservative the colony is brownish grey on the surface, with white points where the spicule-filled lobes of the evenly spaced, stellate branchial apertures open to the surface. Linings of the branchial apertures are black owing to the pigment in the superficial layer of test that turns in to line the siphons. The pigment in the superficial layer of test is mixed with the small spicules and overlies a non-pigmented layer of test. Zooids cross the deep horizontal common cloacal cavities singly or in clumps with dark pigment and sparse spicules mixed in the test connectives that surround them. The abdomina especially are encapsulated in black pigment cells in the test. Common cloacal cavities do not penetrate the test posterior to the zooids, and the basal test is opaque and white with crowded spicules. Spicules are small (to 0.035 mm diameter) and globular with numerous flat-tipped, rod-like rays.

Zooids have eight stigmata in the anterior row and six in the posterior row and a large open atrial aperture without an anterior lip.

Remarks. This specimen has the usual small globular spicules and the black pigment of formerly described specimens, although the black squamous epithelium of the Swain Reefs specimen (see Kott, 2001) has not been detected.

Didemnum candidum Savigny, 1816

( figure 18E )

Didemnum candidum Savigny, 1816: 194 ; Kott, 2001: 157 and synonymy.

Distribution. Previously recorded (see Kott, 2001): Queensland (Low Is), Western Pacific, West Indian Ocean ( Tanzania, Mauritius, Malagasy), Gulf of Suez, Gulf of Arabia. New record: Western Australia (Houtman’s Abrolhos, WAM 557.88).

Description. The newly recorded colony is about 5 mm thick with rounded margins and is smooth on the upper surface. The surface layer of test is thin. The common cloacal cavity is a horizontal space with thoraces crossing it in their own ventral strip of test. Abdomina are embedded in the relatively thick basal layer of test. A single sessile common cloacal aperture is on the surface. Spicules are crowded throughout the colony. They are relatively uniform with five to seven, and occasionally nine short, rod-like rays in optical transverse section. Zooids have a small thorax with a sessile atrial aperture without an atrial lip and a relatively large abdomen containing a long, curved gut loop. A long, tapering retractor muscle projects from about halfway down the oesophageal neck. The undivided testis is surrounded by seven coils of the vas deferens.

Remarks. The specimen is as previously described for this species and the spicules are the usual stellate form with relatively few, short rod-like rays, differing from those previously described only in the maximum spicule size (0.07 mm diameter), which is more than previously reported for this species.

Although previously known from the western Indian Ocean, the Arabian Gulf and its type locality in the Red Sea, this is the first record from the eastern Indian Ocean .

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).