An update on the genus Ischiomysis with a description of I. proincisa sp. nov. (Crustacea, Mysida) from a sublittoral marine cave in the Gulf of Guinea (tropical E-Atlantic)

Ischiomysis proincisa sp. nov. is described from a comparatively large, semi-dark marine cave in sublittoral waters off the small island Ilhéu das Rolas, directly south of São Tomé Island in the Gulf of Guinea. As striking features, the new species is distinguished from both its congeners by an anteriorly incised rostrum in both sexes and by two versus only one modified flagellate spine on the ischium of the eighth thoracic endopod in males. The new species is sympatric yet ecologically remote from the congener I. telmatactiphila , which is associated with the sea anemone Telmatactis cricoides in brighter habitats. New records and morphological notes are given for I. telmatactiphila and I. peterwirtzi . An updated definition of the genus Ischiomysis and a key to its three species are given.