The corallanid isopods, C. nodosa, C. estuaria sp. nov. C. bidentata sp. nov. and C. tridentata sp. nov. have been found within timbers of mangroves and man-made structures in marine and brackish waters around Papua New Guinea. Corallana estuaria, C. bidentata and C. tridentata are new to science and are described in detail. In addition, aspects of the ecology of all four species are considered, including their association with the marine-boring isopods, Sphaeroma terebrans and S. triste.