Semiaquatic bugs (Heteroptera, infraorder Gerromorpha) are distributed worldwide with approximately 1,600 described species. Most species live in various types of freshwater habitats, but a little more than 10% have colonised the marine environment. The Australian fauna constitutes a significantly higher percentage of marine species (about 25%) than in any other continent. Among these are the coral treaders, Hermatobates Carpenter, belonging to the Hermatobatidae, one of very few insect families that only include marine species. In this paper the two species of Hermatobates previously known from Australia are redescribed and H. armatus , sp. nov. from the Chesterfield Islands in the Coral Sea is added. The distribution of species known from Australia and New Caledonia is mapped, and a revised key to the eight species currently recognised in the genus is presented. Finally, the available knowledge about the biology and ecology of coral treaders is reviewed and discussed.