| Summary: | Accurate delimitation of a species’ geographic range is important for conservation planning and biogeography. Geographic range limits provide insights into the ecological and historical factors that influence species distributions (Gaston 1991; Brown et al. 1996), whereas the extent of occurrence of a taxon is a key component of IUCN criteria used for assessing the conservation status of species (IUCN 2001). Freshwater mussels (Unionoida) are an ancient group of palaeoheterodont bivalves that inhabit lotic and lentic freshwater environments on every continent except Antarctica (Graf and Cummings 2006). The Australian Unionoida is represented by the Hyriidae with six genera and 18 species (Ponder and Walker 2003). The Unionoida are distinguished from other bivalves by their larval stage that are, with a few exceptions, are obligate parasites of fish and sometimes amphibians (Watters and O’Dee 1998; Wächtler et al. 2001). All freshwater mussels brood their larvae in specialised regions of the female’s gills known as ‘marsupia’ (Bauer and Wächtler 2001). In the Hyriidae, the marsupia are restricted to the inner pair of demibranchs. An opportunistic stopover along the Great Northern Highway in the eastern Pilbara region (Indian Ocean Drainage Division) of Western Australia revealed the existence of a Lortiella population in the De Grey River, the first record of the genus to occur in the region. Here we identify the species, tentatively, using shell morphology and present new observations of internal anatomy and document the contemporary range of the species’ distributions.
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