Phylogenetic placement of the Neotropical endemic genus Hydrodessus J. Balfour-Browne, 1953 (Coleoptera: Dytiscidae) based on larval morphology

The phylogenetic relationships of members of the hydroporine tribe Bidessini (and particularly of the Neotropical endemic genus Hydrodessus J. Balfour-Browne, 1953) are investigated based on a cladistic analysis of larval characteristics, including 26 Hydroporinae species in 25 genera. For this purpose, the larvae of Hydrodessus latotibialis Miller, 2016 are described for the first time including detailed morphometric and chaetotaxic analyses of the cephalic capsule, head appendages, legs, last abdominal segment and urogomphi. Larval morphology supports a monophyletic origin of the Bidessini based on the absence of the primary pore ABc, a unique feature within Hydroporinae. Hydrodessus was recovered as sister to other Bidessini studied, being characterized by several unique character states. This result supports a previous hypothesis of a basal position of this genus within Bidessini based on adult characters. The presence of natatory setae on femur, tibia and tarsus could represent an adaption to life in lotic environments.