Synoicum vesica, Kott, 2008

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 : 1147-1148

Synoicum vesica sp. nov.

( Figures 7B, C )

Distribution

Type locality: Western Australia CSIRO SS10 / 05 (Pt. Hillier, Stn 57, 117.1970E 35.3735S, 195–196 m, 27 November 2005, holotype WAM Z27524 , QM G328100 ) .

This species is one of three Synoicum spp. taken at this location, the others being S. chrysanthemum and S. implicatum sp. nov.

Description

The holotype colony is a rounded globe about 6 cm in diameter, narrowing to the base by which it is fixed to the substrate. A network of red veins is along each side of circular common cloacal canals, where the zooids open to the surface through the thin surface layer of crowded sand. Internally sand is sparse and the firm gelatinous test is translucent, containing only a scattering of spherical red cells and the long, well-spaced zooids that project into the base of the colony. Common cloacal apertures were not detected.

Zooids are long and narrow. Both apertures have a relatively short muscular siphon. The rim of the branchial aperture has six shallow lobes and the anterior rim of the atrial aperture is produced forwards into a short rounded lip. The branchial sac has up to 20 rows of stigmata with 12 rather short and rounded stigmata in each half row. The length of the stigmata gradually decreases toward the dorsal and ventral midlines. The abdomen is short, although the oesophagus is long. The smooth-walled stomach tapers toward its pyloric end where it merges into the duodenum. The posterior stomach is oval as is the mid-intestine which opens into the rectum in the pole of the gut loop.

Gonads consisting of the longitudinal cluster of male follicles and connected by vasa efferentia are grouped around a single-egg ovary in the middle of a very long posterior abdomen. The long posterior abdomina of most of the zooids are filled with vegetative cells and it is probable that this colony is in a vegetative phase, as evidenced by the small stigmata and the small abdomen and simple gut loop.

Remarks

The tropical Synoicum durum Kott, 1992a and S. suarenum Kott, 1992a from eastern Australia have simple atrial apertures like the present species. The former species also has a sandy external layer of sand like the present species. The latter has a similar long posterior abdomina with a cluster of gonads halfway down but it lacks an external layer of crowded sand. Further, both these species have zooids arranged in circles around central common cloacal apertures rather than lining each side of the common cloacal canals forming a network as in the present species. Synoicum intercedens ( Sluiter, 1909) also has a short atrial siphon and a rounded anterior lip on the anterior rim of the opening, but its almost spherical stomach has pouches in its wall unlike the small smooth pear-shaped stomach of 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.