The discovery of two new non-marine ameirids from the southern Yilgarn region significantly extends the geographic range for this group in Australia and exposes weaknesses in the conservation and environmental impact assessment (EIA) of subterranean species potentially threatened by mining developments. Megastygonitocrella embe, sp. nov. differs from seven previously described Australian congeners by the armature of the second leg endopod and absence of spinules on the somites. A key to world species of Megastygonitocrella is presented. Phylogenetic analysis based on 57 morphological characters and 30 species belonging to the Stygonitocrella s.l. group suggests that Antistygonitocrella pardalotos, gen. et sp. nov. has no close relatives anywhere in the world. Superficial similarities between the two new species are either plesiomorphies or homoplasies. The habitats of these new short-range endemic species are fractured-rock aquifers developed in Archaean greenstone, where the groundwater is characterised by acid conditions, high salinity and low dissolved oxygen. The population of A. pardalotos is threatened by a mining development. Despite the advanced level of environmental protection policy in Western Australia, our taxonomic study highlights limitations in EIA practices and discusses potential improvements which have global relevance in regions where short-range endemics coincide with extraction of mineral resources.