The semiaquatic bugs (Hemiptera : Heteroptera, infraorder Gerromorpha), comprising water striders and their allies, are familiar inhabitants of water surfaces in all continents. Currently, the world fauna has more than 1900 described species classified in eight families and 165 genera. A phylogenetic analysis using maximum parsimony was performed on a dataset comprising 56 morphological characters scored for 24 exemplar genera covering all families and subfamilies of Gerromorpha. The phylogenetic relationships found concur with those presented by Andersen (1982) except that the relationships between some subfamilies of Veliidae and Gerridae are unresolved. The Australian fauna of Gerromorpha comprises six families, 30 genera, and 123 species. One-third of the genera and more than 80% of the species are endemic to Australia. Previously, we have covered all Australian species of the families Gerridae, Hermatobatidae and Veliidae. The present paper deals with the families Hebridae, Hydrometridae, and Mesoveliidae. We offer redescriptions or descriptive notes on all previously described species, describe Mesovelia ebbenielseni , sp. nov. (Mesoveliidae), Austrohebrus apterus , gen. et sp. nov., and Hebrus pilosus , sp. nov. (Hebridae), and synonymise Hebrus woodwardi Lansbury, syn. nov. (Hebridae) and Hydrometra halei Hungerford and Evans, syn. nov. (Hydrometridae). We present keys for the identification of genera and species, and map the distribution of all species. We also give a key for the identification of the families of Gerromorpha known from Australia.