STYELIDAE Sluiter, 1895

Kott, Patricia, 2009, Taxonomic revision of Ascidiacea (Tunicata) from the upper continental slope off north-western Australia, Journal of Natural History 43 (31 - 32), pp. 1947-1986 : 1973-1974

Family STYELIDAE Sluiter, 1895

Type genus: Styela Fleming, 1822 .

Generally members of the family are readily recognized by their simple branchial tentacles, plain-edged dorsal lamina, up to four folds in the branchial sac (although often these are reduced in the small zooids of colonial species), glandular folds in the stomach wall, but no arborescent diverticulum of the gut wall and usually a number of hermaphrodite gonads on each side of the body. The family is diverse, containing commonly recorded solitary species in the genera Styela , Cnemidocarpa and Polycarpa , as well as the colonial sub-families Botryllinae and Polyzoinae and highly adapted deep-water genera including Bathyoncus Herdman, 1882 which lack a perforated pharyngeal wall. Other known genera ( Kott 1985; Monniot C and Monniot F 1990, 1991; Sanamyan KE and Sanamyan NP 2006) with transversely elongated stigmata in branchial walls which lack folds are Bathystyeloides Seeliger, 1904 and Dicarpa Millar, 1955 . The open meshes of the pharyngeal region in Bathyoncus are convergent characters closely resembling those of deep-sea representatives of other genera in a range of families of phlebobranch and stolidobranch species (e.g., Culeolus later) from deep waters of the continental slope and ocean basins ( Monniot C and Monniot F 1991)

Six species of the genus Bathyoncus are now known, they can be divided into two groups, one containing the type species, B. mirabilis Herdman, 1882 and B. lanatus , having long cnemidocarp-type gonads. The other six known species presently assigned to the genus (see Key later) with polycarp-type gonads may justify the erection of a separate genus.

In view of the frequency of reports of the solitary sub-family Styelinae in shallow waters all around the Australian coast and in continental shelf locations in all oceans, it is surprising that only two of the taxa previously reported from the area are present in this collection ( Styela plicata and Polycarpa pigmentata ). The colonial sub-families are not represented at all, and the only representative of the deep-water genera listed previously is the specimen of Bathyoncus lanatus . The new species of Polycarpa has gonads reminiscent of those in Polycarpa perstellata Monniot F. and C., 2003, taken in deep (960 m) waters off Fiji.