We provide an extensive and comprehensive revision of the Australian species of the genus Ozestheria based on an integrative taxonomic approach. In this integrative approach, molecular genetic analyses (COI, 16S and ITS-2) were combined with geometric morphometric analyses of carapace shape, ornamental features and traditional taxonomic assessments including head, thoracopod, telsonic and furcal features as well as carapace length. Initial species delimitation was based on genetic data. Morphometric differences in their carapace shape were then examined and overall morphological differences assessed. The genetic data yielded a high number of previously unknown and morphologically highly similar species. Deciding which of these correspond to the currently known and accepted species or to one of the previously synonymized species or varieties was challenging. Historic type specimens were thus assigned to the respective genetically delimited species with the aid of carapace shape variables as predictors of species identity. The taxonomic descriptions of all known and accepted species are updated based on the original type material (if available). Ozestheria dictyon is treated as a junior synonym of O. lutraria (the original description of O. dictyon was based on juveniles of O. lutraria), O. packardi is treated as a species inquirenda (the original description is inadequate and the types are lost), O. rufa is treated as a valid species (formerly treated as species inquirenda) and three former varieties of O. packardi are raised to full species status: O. cancellata comb. nov., O. minor comb. nov. and O. typica comb. nov. Furthermore, 27 species of Ozestheria new to science are formally described: O. barcaldinensis sp. nov., O. beleriandensis sp. nov., O. bourkensis sp. nov., O. carnegiensis sp. nov., O. christiani sp. nov., O. echidna sp. nov., O. frederikeae sp. nov., O. fuersichi sp. nov., O. gemina sp. nov., O. glabra sp. nov., O. henryae sp. nov., O. jiangi sp. nov., O. jonnae sp. nov., O. marthae sp. nov., O. matuwa sp. nov., O. ngamurru sp. nov., O. paralutraria sp. nov., O. pilbarensis sp. nov., O. quinlanae sp. nov., O. radiata sp. nov., O. richteri sp. nov., O. rincewindi sp. nov., O. selmae sp. nov., O. setifera sp. nov., O. sivesae sp. nov., O. timmsi sp. nov. and O. weeksi sp. nov. With now 38 Australian species of Ozestheria, our results further underline the exceptional diversity of the Australian spinicaudatan fauna, raising the total number of recognized spinicaudatan species to 97, nearly half of their worldwide known species diversity.
