Description of the mature larvae of the halophilic diving beetles Mystonectes coelamboides (Fall, 1923) and M. panaminti (Fall, 1923) and comparison with other known Deronectina (Coleoptera: Dytiscidae, Hydroporinae).

The larval morphology of Mystonectes Fery & Ribera, 2018 is described for the first time based on third instar larvae of the halophilic species M. coelamboides (Fall, 1923) and M. panaminti (Fall, 1923) collected in Death Valley, California (USA). Larvae of these two species differ in some aspects suggesting they are not geographical variants of a single species. Mystonectes larvae share with those of other known Deronectina a synapomorphic very short antennal process (A3) on antennomere 3. With regard to internal Deronectina phylogeny, it appears closely related to Scarodytes Gozis, 1914 and Leconectes Fery & Ribera, 2018 with which they share very elongate legs with natatory setae, very elongate urogomphi, and presence of numerous annuli on urogomphomere 1. Some larval morphological traits suggest a possible phylogenetic relationship between Leconectes and Mystonectes.