Synoicum sphinctorum, Kott, 2006

Kott, Patricia, 2006, Observations on non-didemnid ascidians from Australian waters (1), Journal of Natural History 40 (3 - 4), pp. 169-234 : 200

Synoicum sphinctorum sp. nov.

( Figures 4D–F , 10C )

Distribution

Type locality. South Australia (Kangaroo I. between Western River Cove and Snug Cove, ‘‘ The Arches’ ’, on rock wall, 10–14 m, coll. K. Gowlett Holmes, 14 November 2001, holotype SAM E3283 ) .

Description

The colony is a solid sandy mass, although the sand is crowded only on the surface and is sparse internally. The upper surface has dome-like elevations surrounded by about 10 branchial apertures and with a terminal common cloacal aperture. Broad sandy rounded ridges surround the domes. The branchial apertures are in the groove between the central dome and the marginal rounded ridge. The atrial aperture is on a brown-coloured siphon with a large, rounded muscular atrial lip projecting from the anterior rim of the opening. About three fine-pointed papillae are on the posterior rim of the atrial opening. Distinct sphincter muscles surround the atrial and branchial siphons. Gonads were not detected in the type colony. A small papillum projects from the mid-dorsal line just behind the atrial opening. The zooids are obscured by the sand on the colony. The branchial sac has 18 rows of stigmata with about 20 in each half row. The anus opens level with the seventh row of stigmata. The stomach is relatively small with 12 shallow, internal longitudinal folds, although these are not always seen in smaller zooids. Gonads were not detected, but the posterior abdomen is present with two narrow longitudinal muscles from the thorax extending along it.

Remarks

Although the zooids and the systems are like those of S. concavitum Kott, 1992a , the sphincter muscles around the siphons are more conspicuous and the colony has more sand. Synoicum obscurum Kott, 1992a has different colonies with two or three systems per lobe and only irregular creases (rather than longitudinal folds) in the stomach wall. The larva of the present species is not known.

Figures

Figure 4. (A–C) Synoicum citrum (holotype SAM E3287): (A) colony; (B) thorax showing branchial sac; (C) whole zooid showing longitudinal muscles. (D–F) Synoicum sphinctorum (holotype SAM E3283): (D) colony; (E) thorax; (F) abdomen and posterior abdomen. Scale bars: 1 cm (A); 0.2 mm (B, C, E, F); 2 mm (D).

Figure 10. In situ images of: (A) Synoicum sacculum (SAM E2864); (B) Synoicum sacculum (SAM E3288); (C) Synoicum sphinctorum (SAM E3283); (D) Aplidium abditum (SAM E3268); (E) Aplidium brevilarvacium (SAM E3284); (F) Aplidium clivosum (SAM E3390); (G) Ascidia scaevola (SAM E2871); (H) Botryllus stewartensis (SAM E3289).