Stygofauna are animals inhabiting groundwater. Stygofauna are typically pale and blind with elongated appendages, resulting from their subterranean existence. Most stygofauna are invertebrates, predominantly crustaceans, but also worms, snails, water mites and diving beetles, although some fish are also stygofauna.

Stygofauna occupy groundwater across a diverse range of  environments including caves, aquifers, and springs. They may be found in deep groundwater habitats tens to hundreds of metres below the surface, in addition to shallow groundwater habitats including springs and spring-brooks where groundwater discharges to the surface. They also occur in hyporheic and parafluvial setting (saturated sediments beneath and alongside surface water courses). Stygofauna are found in oxygenated groundwater ranging from fresh to brackish in salinity, but they may occur in salinities up to seawater, and occasionally in salinities twice that of seawater.

In Western Australia, stygofauna have been documented from most regions and areas including the Kimberley, Pilbara (Pilbara craton and Barrow Island), Carnarvon (Cape Range), Murchison, Goldfields, South West (Perth Basin and Leeuwin Naturaliste Ridge), South Coast (Albany and Nullarbor Plain). In the Pilbara region, sampling conducted in the last decade has revealed the Pilbara to be a globally significant hotspot for stygofauna diversity (Humphreys 2000; Eberhard, Halse and Humphreys 2006). Stygofauna is widespread and occurs in a range of hydrogeological environments including karst, fractured rock, vuggy pisolite and porous aquifers, in addition to springs, parafluvial and hyporheic environments (Eberhard  et al. 2005).