Testing the monophyly of the tribe Aciliini and the phylogenetic position of the Afrotropical genus Aethionectes Sharp, 1882 (Coleoptera: Dytiscidae, Dytiscinae) based on larval morphology.

We describe the instar III larva of the Madagascar endemic diving beetle Aethionectes oberthueri (Rgimbart, 1895), including detailed morphometric and chaetotaxic analyses of the cephalic capsule, head appendages, legs, terminal abdominal segment and urogomphi in order to discover useful characters for distinguishing Aethionectes Sharp, 1882 larvae from those of other known Aciliini genera (Coleoptera: Dytiscidae, Dytiscinae) i.e., Acilius Leach, 1817, Graphoderus Dejean, 1833, Rhantaticus Sharp, 1882, Sandracottus Sharp, 1882, and Thermonectus Dejean, 1833. A parsimony analysis based on 94 larval characteristics was conducted using the program TNT. The larva of Aethionectes is similar in every way to those of the other Aciliini genera adding to the unique morphology of members of this lineage. Whereas Acilius larvae stand out from other genera, our parsimony analysis did not recover any clear phylogenetic position of Aethionectes within the tribe. A key of identification of instar III larvae of World Aciliini is provided.