Ancyronyx clisteri, a new spider riffle beetle species from Borneo, redescription of A. sarawacensis Jäch including a description of the larva and new distribution data for A. procerus Jäch using DNA barcodes (Coleoptera, Elmidae).

Ancyronyx clisteri sp. nov. (Coleoptera, Elmidae) a new spider riffle beetle discovered from northern Borneo (Brunei; Sabah and Sarawak, Malaysia) and the larva of Ancyronyx sarawacensis Jäch are described. Illustrations of the habitus and diagnostic characters of the new species and the similar and highly variable A. sarawacensis are presented. Differences to closely related species, based on DNA barcodes and morphological characters, are discussed. Association of the larva and the imago of A. sarawacensis, and the occurrence of Ancyronyx procerus Jäch in Peninsular Malaysia and Sabah are confirmed by using COI mtDNA sequences.