Systematics of the Phreatoicidea

We provide a new cladistic analysis of the Phreatoicidea, revising previously employed characters and including additional generic exemplars. This analysis reinforces the conclusion that many currently recognized families and subfamilies are not monophyletic. The ‘primitive’ family Amphisopodidae is paraphyletic and the Nichollsiidae (with species from India) appears to be a clade within the Australian subfamily Hypsimetopodinae. The results also suggest changes to the composition of some subfamilies. By removal of the southeastern Australian genus Crenoicus, the Phreatoicinae is restricted to New Zealand taxa. Approximate ages of tectonic rifting of the super-continent Gondwana were used to biogeographically constrain the timing of events in phreatoicidean phytogeny. Because the Indian genus Nichollsia is nested within the Australian Hypsimetopodinae, this clade has a minimum age of 130 million years. Phreatoicidean isopods were classified into three ecotypes: surface-cryptic, surface-burrower, and groundwater dwelling forms. The phylogenetic distribution of these ecotypes provides evidence for at least two separate colonizations of groundwater habitats. One colonization may be older than the rifting of Indian subcontinent and the other is approximately dated by the separation of New Zealand from East Gondwana. The phylogenetic age, endemism and localized diversity of phreatoicidean isopods confer a high conservation value upon this group. This phylogenetic and biogeographic knowledge of phreatoicidean isopod crustaceans may assist informed decisions on their conservation.