A genetic assessment of the taxonomic status of New Zealand mussels of the genus <i>Xenostrobus</i> Wilson, 1967

The genus <i>Xenostrobus</i> consists of small, marine and estuarine mussels that all appear similar externally. One of its estuarine species, <i>Xenostrobus securis,</i> with a native range in New Zealand and Australia, has become invasive in the Northern Hemisphere. No genetic data are available to determine if <i>X. securis</i> populations from the two countries are conspecific. Additionally, marine <i>Xenostrobus</i> from New Zealand have often been regarded as a species, <i>X. neozelanicus,</i> distinct fromthe marine Australian species <i>X. pulex</i>. We combined new DNA sequences with published data to assess the taxonomic status of New Zealand <i>Xenostrobus.</i> The data comprised 658 aligned bases of mitochondrial cytochrome <i>c</i> oxidase subunit I (COI) gene and 331 bases of nuclear histone H3. There was no evidence that <i>X. securis</i> populations from Australia and New Zealand are specifically distinct. Northern Hemisphere specimens of <i>X. securis</i> belonged to Australian, not New Zealand, clades in phylogenetic analyses of COI data, suggesting the former country as their more likely original source. The results confirm that <i>X. neozelanicus</i> and <i>X. pulex</i> are distinct species and for nomenclatural completeness for this taxonomic decision a lectotype is designated for <i>Mytilus ater</i> Zelebor in Dunker and Zelebor, 1866 [ = <i>Modiolus neozelanicus</i> Iredale, 1915].