Phylogenetic Placement of the Genus Sternhydrus (Coleoptera: Dytiscidae: Cybistrini) Based on Larval Morphology, with Description of S. atratus

The phylogenetic relationships of the Australasian diving beetle genus Sternhydrus Brinck, 1945 were studied based on a cladistic analysis of 16 taxa and 112 morphological larval characters. Larvae of S. atratus (F., 1801) were described and illustrated in detail with particular emphasis on morphometry and chaetotaxy. Primary chaetotaxy were unknown for the genus. The results supported the inclusion of Sternhydrus in a clade of Australian Cybistrini genera along with Onychohydrus Schaum and White, 1847 and Spencerhydrus Sharp, 1882 based on four synapomorphies: presence of additional pores on antennomere 1, tibial seta TI7 short and spine-like, and urogomphi longer than broad, included in the nonsclerotized ventrodistal area surrounding the anus. A sister group relationship of Sternhydrus and Onychohydrus is suggested by two synapomorphies: lateral projections of frontoclypeus serrate, and row of additional anteroventral setae on meso- and metatarsus composed of several thin setae of variable length. The genus Sternhydrus is characterized by two autapomorphies: presence of both spine-like and hair-like additional setae on the ventral surface of the femur, and absence of primary pores on the urogomphus.