Synoicum sphinctorum Kott, 2006

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 : 1145-1147

Synoicum sphinctorum Kott, 2006

( Figure 7A )

Synoicum sphinctorum Kott 2006, p. 200 .

Distribution

Previously recorded (see Kott 2006): South Australia (Kangaroo I.). New record: Western Australia, CSIRO SS10 /05 (Albany, Stn 22, 100 m, 22.11.05, G328068) .

The only known records of this species from two widely separated locations off the southern coast of the continent may represent the eastern and western limits of its range.

Description

The colony is a large, firm dome, with a smooth, even external surface. It is about 5 cm high and is fixed by the whole of the flat, irregular and sandy base, which is about 8 cm in diameter. A thin layer of sand is in the surface test around the upper surface of the colony. The internal test is firm but glassy and transparent and has only sparse sand embedded in it. Zooids are robust. A distinct sphincter is around the top half of the tulip-shaped branchial siphon. The atrial siphon is also surrounded by a broad sphincter muscle. A conspicuous atrial lip is produced from the anterior margin of the aperture. A small dorsal papillum projects from the median line just behind the atrial siphon. The branchial sac has stigmata in about 22 rows with about 20 in each half row. The wall of the small, elongate stomach has about 12, sometimes branched, longitudinal tracts of glandular epithelium but these are not the distinct folds of the stomach wall that are characteristic of the genus Aplidium . Bunched testis follicles behind a small ovary are in the anterior part of the posterior abdomen. In these zooids the thorax and the abdomen and the abdomen and posterior abdomen respectively are separated by a constriction of the body wall. Up to three larvae are being incubated in the base of the atrial cavity of some of the zooids. The trunk is 1.0 mm long and a mass of epidermal vesicles is in the larval test around the anterior half of the trunk which project back to the posterior end of the

trunk along the median ventral and dorsal lines. The tail curves about three-quarters of the way around the trunk.

Remarks

The zooids of the present species are characteristic of the majority of the species in this genus, with the atrial tongue projecting out from the anterior rim of the aperture, rather than from the body wall anterior to the opening as it does so often in Aplidium . Also the dorsal papillum is characteristic of (though not exclusive to) Synoicum . The longitudinal tracts of epithelium lining the stomach wall can be mistaken for stomach folds, although careful examination shows that although they protrude slightly into the stomach, the stomach wall itself is not folded. The constrictions of the body wall between thorax and abdomen and abdomen and posterior abdomen are reminiscent of similar constrictions in Aplidiopsis . However the only similar species of Aplidiopsis , A. sabulosa , has a mulberry-like stomach. The constrictions in the present zooids could be artefacts.

Kott (2006) found surface features associated with separate circular systems in the types of this species (from Kangaroo I.). These were not detected in the present specimen, in which indications of the form of the systems were not detected amongst the sand that adheres to the surface. Other features of the zooids are similar. The species is distinguished from others in this genus by the absence of a mulberry-like pattern of pouches in the stomach wall, the simple dome-shaped colony without sand in the internal test and the large larval trunk with crowded epithelial vesicles in the larval test (reminiscent of the larvae of some species of Aplidium ). The bunched male follicles have been reported in some of the zooids of the Western Australian Synoicum atopogaster Kott. 1992a and appear to be dependent on the state of contraction of the posterior abdomen (see Synoicum atopogaster Kott, 1992a ). The latter species also resembles the present one in having numerous vesicles in the larval test but lacks the distinctive protruding atrial siphon of the present species and its larva has median ampullae between the adhesive organs that were not detected in the present species.

Figures

Figure 7. Synoicum sphinctorum (QM G328068): A, larva. Synoicum vesica sp. nov. (QM G328100): B, colony; C, zooid. Aplidium clivosum (QM G328133): D, colony. Aplidium crateriferum (E1–2 QM G328113; F, G, QM G328111): E1–2, colonies; F, thorax and abdomen; G, posterior abdomen showing male follicles. Scales: A, C, F, G, 0.2mm; B, D, E, 1.0 cm.