Four new species of the genus Cytheropteron (Ostracoda) are described from the Tasman and Coral Seas. These new species (C. delphinum, C. hikurangiensis, C. sarsi and C. taciturnum) are closely related to the cosmopolitan, "cold-water" form Cytheropteron testudo Sars 1869, which is redescribed. A precise taxonomic definition of Cytheropteron testudo is made difficult by the fact that Sars' type material has been lost. However, from the present study it is apparent that Cytheropteron perlaria Hao 1988 also occurs in many Northern Hemisphere samples. To date most workers have not been able to discriminate that taxon from the more ubiquitous Cytherpteron testudo. In Southern hemisphere deep-sea samples, confusion may also arise between C. testudo and C. wellmani Hornibrook 1952. A re-examination of topotypic material and fossil and recent specimens from the New Zealand region has led to a redefinition of key carapace characters of C. wellmani and thus allows that species to be more easily discriminated from C. testudo
