Phreatoicidea Stebbing, 1893 live in freshwaters of Gondwana: Australia, South Africa, India and New Zealand. Many of these isopods have a subterranean lifestyle. Parsimony analysis of morphological data of generic exemplars and a Triassic fossil was used to explore the timing of this habitat adaption. The monophyly of the Hypsimetopidae Nicholls, 1943, including blind taxa Hyperoedesipus Nicholls & Milner, 1923 (Western Australia), Nichollsia Chopra and Tiwari, 1950 (Ganges Plain, India) and Phreatoicoides Sayce, 1900 (Tasmania and Victoria) was strongly supported. Crenisopus Wilson and Keable, 1999 (Kimberleys, Western Australia) and the Ponderellidae Wilson & Keable, 2004 (Queensland mound springs) may be sister to hypsimetopids. Blind Phreatoicidae found only in south-eastern Australia and in New Zealand were also monophyletic. The hypogean habitat, blindness, fossil and plate tectonic evidence were mapped on the cladogram to estimate timing of this adaptation. A subterranean adaptation before 130 million years ago was supported for hypsimetopids. Phreatoicus Chilton, 1891 and Neophreatoicus Nicholls, 1944 (hypogean in New Zealand) were in a monophyletic clade with epigean Phreatoicidae, Crenoicus Nicholls, 1944 (south-eastern Australia) and Notamphisopus Nicholls, 1943 (New Zealand). Blindness in epigean taxa is consistent with recolonisation of surface waters from underground refuges. Because Crenoicus is sister-group to the New Zealand clade, and because overseas dispersal between Australia and New Zealand is unlikely, the minimum age for these blind phreatoicids is ~80 million years. This evidence is consistent with a subterranean freshwater fauna surviving the presumed Oligocene inundation of New Zealand.