text: The genus Ancyronyx was established in 1847 by the German entomologist Wilhelm Ferdinand Erichson based on the type species Macronychus variegatus first described in 1824 by the German coleopterologist Ernst Friedrich Germar. It was regarded as a monotypic species until the French entomologist Antoine Henri Grouvelle described the second species, A. acaroides in 1896. It is the sole member of the tribe Ancyronychini, and is classified under the subfamily Elminae of the riffle beetle family, Elmidae.