Sigillina pulvinus, KOTT, 2003

KOTT, PATRICIA, 2003, New syntheses and new species in the Australian Ascidiacea, Journal of Natural History 37 (13), pp. 1611-1653 : 1618

Sigillina pulvinus sp. nov.

(figure 1C, plate 1A)

Distribution. Type locality: Tasmania (Tasman Peninsula, Waterfall Bay outside Cathedral Cave in ledge in rock wall 10–13 m, coll. K. Gowlett Holmes, 21 October 94, syntypes SAM E2845). There are no further records.

Description. Colonies are circular cushions with rounded margins, to 2 cm diameter. In life they are pinkish white with red zooids, their apertures showing at the surface and the zooids showing through the otherwise white, translucent test. Zooids, evenly spaced about 3 mm apart, are robust, 4–5 mm long (even when contracted). The abdomen and posterior abdominal stolon are about equal in length and the contracted thorax is shorter. Both apertures, on short cylindrical siphons each with six pronounced lobes around the opening, are anterior, on the upper surface of the colony. About 15 parallel muscle bands on each side of the thorax continue in a wide ventral band on the abdomen and the posterior abdominal stolon, surrounding the latter in longitudinal muscles. At each side of the distal extremity of the stout posterior abdominal extension, the muscles from each side are inserted into a small projecting horn from which the tips of the muscles project as sharp points. Three rows, each of about 16 long rectangular stigmata, are in the branchial sac.

The descending limb of the gut loop consists of the oesophagus, an almost spherical, smooth stomach about half-way down the abdomen and a cylindrical duodenum and posterior stomach separated from each other and from the rectum by a short length of mid-intestine. The rectum is a long cylindrical tube occupying the whole ascending limb of the gut loop. Two large epicardial tubes, one each side of the ventral mid-line, extend through the abdomen and the one on the left projects down into the posterior abdominal vascular stolon. A single, large, yolky, spherical embryo, nearly 1.5 mm in diameter, with an ocellus, a small otolith and the tail wound all the way around the trunk, is in a brood pouch separated from the posterior end of the dorsal border of the thorax by a narrow constriction. These embryos are not sufficiently advanced to determine the form of other larval organs. Although embryos are in the brood pouch, gonads were not detected in these specimens.

Remarks. The zooid is characteristic of this genus with a pronounced posterior abdominal stolon, three rows of stigmata, a brood pouch, a relatively short abdomen with a smooth spherical stomach half-way down it and parallel longitudinal thoracic muscles without conspicuous transverse ones. Despite the absence of gonads in the gut loop, the heart at the end of the abdomen and the smooth spherical stomach distinguish these specimens from Pseudodistoma (see Kott, 1992a).

The circular colonies are more regular than the irregular ones of the South Australian S. fantasiana , which also is distinguished by the presence of more than one embryo developing in the less constricted brood pouch and without longitudinal muscles on the posterior abdominal stolon. The species most closely resembles the tropical S. signifera , but it has more regular colonies and smaller zooids. Like S. signifera , the species appears to be a member of the cyanea group of species (see Kott, 1992a) with a large posterior abdominal stolon with conspicuous muscles on it. Other Sigillina spp. have similar zooids, but different colonies.