First Molecular Evidence for Underestimated Biodiversity of Rhachotropis (Crustacea, Amphipoda), with Description of a New Species

The crustacean genus Rhachotropis has a worldwide distribution and amongst the largest bathymetric range known from any amphipod genus. DNA barcoding of new material from around New Zealand and the Ross Sea indicated depth-related biogeographic patterns. New Zealand Rhachotropis do not form a monophyletic clade. Species from bathyal depths on the Chatham Rise, east of New Zealand, show lower sequence divergence to bathyal species from California and the Arctic than to abyssal New Zealand species. Species sampled in the Kermadec Trench, north of New Zealand below 5000 m, seem to be more closely related to Ross Sea abyssal species than to the New Zealand shelf species. The worldwide geographic and bathymetric distribution for all Rhachotropis species is presented here. Depth may have a greater influence on phylogeny than geographic distance. Molecular and morphological investigations of Rhachotropis specimens from the Chatham Rise, New Zealand revealed a species new to science which is described in detail, including scanning electron microscopy. This increases the number of described species of Rhachotropis to 60 worldwide.