Arid northwestern Australia contains one of the world’s more diverse subterranean faunas including many relict obligate groundwater (stygo-) faunas in karst and calcrete aquifers, principally crustaceans, with affinities pertinent to Tethys, and to Pangaea and its derived landmasses. Higher order taxonomic groups are present that are elsewhere unknown in Australia (order Spelaeogriphacea) or in the southern hemisphere (class Remipedia, order Thermosbaenacea), as well as a number of genera ancestral to the main Australian diversification. Many are found in aquifers that are the principal water supply in this arid region and are vulnerable to pollution, water abstraction and dewatering operations.