Under Surveyed and Under Pressure: Additional Biodiversity Uncovered in the Freshwater Mussels (Unionida: Velesunioninae) of North‐Western Australia

ABSTRACT Accurate species delimitation underpins freshwater biodiversity assessment and conservation, yet taxonomic uncertainty remains a major impediment for many invertebrate groups. Velesunioninae (Unionida; Hyriidae) constitutes the most diverse group of Australian freshwater mussels but is poorly documented in the Kimberley and Pilbara regions of north‐western Australia, where only three species have been reported across an area spanning ~930,000 km 2 . These distributions have historically been inferred from shell morphology, despite evidence that shell characters can overlap among species and that genetic data have identified species complexes elsewhere in Australia. Here we integrate genetic and morphological data to test for the presence of undescribed species within Velesunioninae collected from five drainages across north‐western Australia. Phylogenetic analyses of multi‐locus molecular data ( COI , 16S , 28S and 18S ) identified five discrete lineages, including one described species ( Lortiella froggatti ), one previously recognised undescribed lineage ( Velesunio ‘sp. Lineage A’) and three previously unknown lineages. Except for L. froggatti which displayed a distinct shell morphology, morphological characters were unreliable in distinguishing Velesunio lineages. Velesunio ‘sp. Lineage A’ and L. froggatti were identified across large geographic distances (1320 km and 550 km, respectively), while the three novel Velesunio lineages showed more restricted distributions. Overall, our results suggest that the apparently widespread morpho‐species previously reported from north‐western Australia may instead comprise complexes of both broadly distributed and geographically restricted undescribed taxa. Further targeted genetic surveys will be necessary to clarify species distributions and support conservation management of freshwater mussels in a region increasingly affected by water extraction and mineral development.