Abstract
A new calanoid copepod, Ridgewayia stygia, is described from a submarine cave in Palau in the Western Pacific. The new species is most similar to a Caribbean species, R. fosshageni, but can be distinguished from the latter by the location of the female genital operculum and the structure of the fifth legs of both sexes. The affinities of the new species appear to lie with the North Atlantic/Mediterranean R. marki species-group rather than the Indo-West Pacific R. typica species-group. This discovery suggests that, within the Tethys Sea, westward dispersal of marine copepods from the Caribbean Province extended as far as the western Central Pacific rather than only to the eastern Central Pacific.
