Description of the glochidia of Alathyria pertexta pertexta Iredale, 1934 (Bivalvia : Hyriidae) from south-eastern Queensland

Abstract

Most freshwater mussels (Bivalvia: Unionida) have larvae (glochidia in Margaritiferidae, Hyriidae and Unionidae) that are parasitic on fishes. Mechanisms of glochidia release and morphological features (size, shape, larval teeth, etc.) vary across taxa and geography. Among the Australasian Hyriidae, glochidia have been described from 12 of the 28 putative species. Alathyria pertexta Iredale, 1934 is a widespread species from subtropical/semitemperate south-eastern Queensland and northern New South Wales to the northern wet tropics of Queensland and southern New Guinea. Little information is available on its biology and its glochidia have not been described in detail. The aim of this study was to describe the glochidia of A. pertexta pertexta and the method of their release. Gravid females collected from Mary River, near Kenilworth, and Isaac River, north-west of Rockhampton, Queensland, released glochidia in ‘amorphous mucus conglutinates’, in which glochidia are released from exhalent siphons of females in a loose mucus matrix that dissociates in water, during the austral spring (August–October); they then hatched from vitelline membranes but remained tethered by a larval thread and began characteristically ‘winking’. Shells (n = 80) are subtriangular and scalene in shape, 268.1 µm long (±1.21, s.e.), 242.9 µm high (±1.22, s.e.) and have a hinge length of 191 µm (±0.63, s.e.). Larval teeth are spineless, S-shaped hooks with singular interlocking cusps on opposing valves. The surface of the apex and valve margins are crenulated, and valves are smooth and porous, held together by a hinge and a singular internal adductor muscle.