Synoicum obscurum Kott, 1992

Kott, Patricia, 2008, Ascidiacea (Tunicata) from deep waters of the continental shelf of Western Australia, Journal of Natural History 42 (15 - 16), pp. 1103-1217 : 1140-1141

Synoicum obscurum Kott, 1992

( Figure 5H )

Synoicum obscurum Kott 1992a, p. 496 .

Distribution

Previously recorded (see Kott 1992a): Victoria (Bass Strait, off Lakes Entrance); New South Wales (Arrawarra). New record: Western Australia CSIRO SS10 / 05 (Bald I., Stn 35, 200 m, 24.11.05, QM G328459 ) .

The species appears to be an indigenous Australian temperate species with a possible range around the southern half of the continent.

Description

The newly recorded colony is a number of sandy lobes branching from a common basal stalk. The terminal part of each branch is an inverted cone, with a circular, slightly concave upper surface gradually narrowing to a thick stalk that is about the same length and half its diameter. Sand is embedded in the brittle external test over the terminal cone where the thoraces of the zooids are accommodated but it is not in the thin partitions of the test that separate the zooids from one another. However, sand is crowded in the basal stalk of the colony where the thin abdomina and posterior abdomina penetrate the solid test. The surface test is slightly raised over the anterior end of each of up to eight zooids that form a circle around the outer margin, surrounding the central depression where the common cloacal cavity has a sessile opening. A terminal six-lobed branchial opening is on a short siphon. The atrial opening, on the antero-dorsal corner of the body, has a muscular lip (contracted in these specimens) with three pointed lobes along its distal margin. The lip is inserted into the margin of the common cloacal aperture. Fine longitudinal muscles, about 20 from the branchial siphon and about five finer ones from the atrial siphon, extend the length of the thorax and continue in a narrow band along the threadlike abdomen and posterior abdomen. Fine transverse muscle fibres in each transverse vessel extend out into the body wall ventrally and dorsally. The thorax is long with 12 rows of 25 stigmata in each half row in the anterior part of the branchial sac although the rows become shorter toward the posterior end of the pharynx. Small papillae, about 12 per row, are on each transverse vessel. The abdomen is about one-third of the length of the thorax and is narrow with a tight vertical gut loop. The small, narrow, smooth walled stomach is about halfway down the descending limb of the gut loop. The posterior abdomen is long and thread-like, many times the length of the rest of the zooid. Testis follicles are in either a single or a double row and a small ovary with five or six eggs is at the anterior end of the testis follicles. About three embryos at different stages of development are in the posterior end of the atrial cavity.

Remarks

The species has a characteristic appearance, the newly recorded colony closely resembling the previously reported material from the eastern seaboard of the continent, the only difference being that the latter have more compacted colonies with the lobes being more tightly bound together, adjacent lobes both adhering to the same grain of sand. The external appearance of the colonies most resembles Polyclinum orbitum Kott, 1992a and Ritterella papillata Kott, 1992a , both of which have similar colonial systems but are distinguished by genetic characters of their zooids. The former species has more numerous branchial papillae, a twisted gut loop and a constriction at the anterior end of the posterior abdomen and the latter species has a folded stomach wall. Branchial papillae, though previously not recorded for this genus, now are known to occur in many species (see above)

Figures

Figure 5. Synoicum implicatum sp. nov. (QM G328098): A, colony; B, thorax and abdomen; C, antero-dorsal part of thorax. Synoicum laboutei (QM G328443): D colony; E, thorax and abdomen, both very much contracted. Synoicum macroglossum (QM G328104): F, thorax; G, abdomen and posterior abdomen. Synoicum obscurum (QM G328461): H, larva. Scales: A, D, 2.0 cm; B, 1.0 mm; C, E–G, 0.5 mm; H, 0.1 mm.