Cumaceans are small, benthic marine crustaceans ranging in size from 1 mm-3 cm. Currently, there are 8 recognized families: Bodotriidae, Ceratocumatidae, Diastylidae, Gynodiastylidae, Lampropidae, Leuconidae, Nannastacidae, and Pseudocumatidae. The Gynodiastylidae is a relatively small family, with 58 published species, and is primarily found in the Southern Hemisphere. Investigation of the collections of the Museum Victoria, Australian Museum, and South Australian Museum yielded six new genera and 45 new species, the majority of them from the Bass Strait region, demonstrating remarkable diversity for a single oceanographic biogeographic province.

In addition, a computer-assisted cladistic analysis of morphological characters at the generic level was undertaken, using the programs PAUP and MacClade. Monophyly of the Gynodiastylidae is supported in all 18 most parsimonious trees, and two distinct subclades are supported in all trees, a Dicoides clade and a Gynodiastylis sensu stricto clade. The relationships of the three most plesiomorphic genera are not well resolved in the analysis.