Larval morphology of four genera of the tribe Hyphydrini Sharp (Coleoptera: Dytiscidae: Hydroporinae) with an analysis of their phylogenetic relationships

Description of structures of the larvae of 4 genera (Desmopachria Babington, Hyphydrus Illiger, Microdytes Balfour-Browne, and Pachydrus Sharp) of the tribe Hyphydrini Sharp is presented. The chaetotaxy and porotaxy of the cephalic capsule, head appendages, legs, last abdominal segment, and urogomphi are discussed in detail. Within the subfamily Hydroporinae, the Hyphydrini are hypothesized to constitute a monophyletic assemblage based on the following 7 synapomorphies: (1) absence of pore PAj, (2) epicranial plates meeting at the ventral midline, (3) absence of pore FRb, (4) medioventral position of seta FR6, (5) absence of pore ANh, (6) abdominal segment 6 sclerotized ventrally, and (7) proximal insertion of the primary seta UR8 on urogomphomere 2. It is proposed that Pachydrus occupies a basal position within the Hyphydrini. A monophyletic origin is indicated for Macrodytes, Desmopachria, and Hyphydrus based on the shared presence of an elongated prementum and a more proximal insertion of seta UR8 on urogomphomere 2. Desmopachria and Hyphydrus are related phylogenetically by the absence of lateral notches on the frontoclypeus, the presence of at least 1 secondary seta on ventral surface of the siphon (3rd instar), and the short and spiniform appearance of the primary seta UR5 in 1st instars.