Extant species are confined to freshwater environments in South Africa, India, and Oceania.

[2] This seemingly Gondwana-derived distribution belies the fact that the group once had a cosmopolitan distribution; fossils which can be assigned to the Phreatoicidea are the oldest isopod fossils, and are found throughout the world.

[3][4] In the intervening 325 million years, phreatoicideans have changed little, and are thus considered living fossils.

[5] The first Australian phreatoicidean was described by Charles Chilton in 1891.

[5] Two families are represented in Australia: Amphisopodidae in the interior of Australia, and in the west, and Phreatoicidae in New South Wales, Victoria and Tasmania.