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We report the discovery of a new species of Copelatus that is morphologically highly modified for life in groundwater. Copelatus abditus sp.n. was collected from a 4 m deep bore in central Australia. It was placed in Copelatinae based on morphological evidence. This is the first known stygobiont diving beetle that does not belong to the subfamily Hydroporinae. Sequences from the mitochondrial DNA cytochrome oxidase 1, 16S rRNA, tRNAL and NADH dehydrogenase subunit 1 genes suggest that the species belongs to the subgenus Papuadytes, the morphological apomorphies of which are reduced in the new groundwater species. Copelatus (Papuadytes) abditus very much resembles other world stygobiont dytiscids, which all belong to the subfamily Hydroporinae. We suggest that this striking convergence is due to similar selective pressures imposed on all groundwater beetles. We suggest a scenario in which species from temporary habitats evade drought by entering the hyporheic zone, and may be driven to a subterranean existence by desertification of their ancestral habitats, as can be observed in Australia.