Sacoglossa (=ascoglossa) (mollusca, opisthobranchia) from southern Western Australia

Abstract

Seven species of the opisthobranch order Sacoglossa (=Ascoglossa) are recorded from southern Western Australia. Three of these are shelled species. Ascobulla fischeri (Adams and Angas, 1864) and Oxynoe viridis (Pease, 1861) are redescribed, and Volvatella ventricosa n. sp. is described as the third green species of Volvatella. In the Elysiidae, Elysia australis (Quoy and Gaimard, 1832) is redescribed. A new species, Elysia filicauda, with an extremely long, thread-thin tail, is also described. It feeds on the siphonalean green alga ? Acetabularia peniculus and has a unique method of copulation. Elysiella pusilla Bergh, 1872, is identified as a senior synonym of Elysia halimedae Macnae, 1954. Its radular teeth are peculiar in having narrow, hollow cusps with unilateral denticles. A new species of the rare genus Pattyclaya, P. brycei n. sp., is also described. It has numerous transverse lamellae containing branches of the digestive gland on the distal, inner surface of the parapodia. Its radular teeth are blade-shaped and smooth. The Sacoglossa (=Ascoglossa) are almost exclusively herbivorous opisthobranchs, feeding on the cell sap of algae or seagrasses. The Sacoglossa comprise shelled as well as non-shelled species. Some shelled species have a well-developed shell into which the animal can withdraw completely. Others have a reduced shell covering only the visceral mass, and a few have a bivalved shell.