Aplidium abditum, Kott, 2006

Kott, Patricia, 2006, Observations on non-didemnid ascidians from Australian waters (1), Journal of Natural History 40 (3 - 4), pp. 169-234 : 201-203

Aplidium abditum sp. nov.

( Figures 5E, F , 10D )

Distribution

Type locality. Tasmania ( Port Davey , 6–8 m, coll. K Gowlett Holmes, 12 March 2003, holotype SAM E3268 ) .

Description

A whitish, flattened, sandy colony with numerous zooids and common cloacal systems. Zooids are along each side of the narrow common cloacal canals that appear to converge to the numerous common cloacal apertures, which sometimes are conspicuous, sessile openings, or they are on the top of slight surface elevations. The translucent zooids sometimes look black owing to the black faecal pellets in their gut. However, there also are some black spherical bodies in the test over the zooids. Zooids have a long pointed atrial lip arising from the upper rim of the atrial aperture. Muscles are relatively delicate. The thorax is long with 11 rows of about eight stigmata per side, a short stomach with five longitudinal folds is in the abdomen. The posterior abdomen is short with bunched testis follicles. Two to four cigar-shaped larvae are being incubated in the atrial cavity. The larval trunk is 0.44 mm long and the long tail is wound about three-quarters of the way around the trunk. Single median ampullae alternate with the three antero-median adhesive organs and epidermal vesicles were not detected.

Remarks

The Gulf of Suez/Red Sea tropical species, Aplidium lobatum Savigny, 1816 has similar cloacal systems, the same number of rows of stigmata, and a short posterior abdomen with bunched testis follicles like the present species, although it has more stigmata and the present species appears to be a temperate one. Aplidium ritteri ( Sluiter, 1895) is a tropical species with a similar branchial sac, small zooids, five stomach folds, and testis follicles bunched in the posterior abdomen, but its larva is more decorated than the present species, having crowded epidermal vesicles. The present species is distinguished by its relatively small branchial sac, short posterior abdomen with bunched male follicles, and small larvae with median ampullae but without lateral ampullae or epidermal vesicles.

Figures

Figure 5. (A–D) Synoicum syrtis (holotype QM G308757): (A) thorax; (B) abdomen; (C) anterior part of posterior abdomen; (D) end of posterior abdomen. (E, F) Aplidium abditum (holotype SAM E3268): (E) whole zooid; (F) larva. Scale bars: 0.2 mm (A–E); 0.1 mm (F).

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).