We describe a new genus and species of ascid mite, Arrhenoseius gloriosus gen. et. sp. nov., from rainforests in Queensland, Australia. This heavily armoured predatory mite can complete a generation in less than a week when fed with nematodes at 25 deg C. The new genus belongs to the tribe Blattisociini and appears to be most closely related to the northern hemisphere genus Zercoseius. However, unlike other Blattisociini for which the sex determination mechanism has been determined, A. gloriosus is arrhenotokous instead of pseudoarrhenotokous. We describe the sexual dimorphism in the deutonymphal instar and ontogenetic changes in the form of tarsal setae of legs II-IV. These attributes have not been previously noted among mites of the family Ascidae.