Larval morphology of Ilybiosoma Crotch, 1873 (Coleoptera: Dytiscidae: Agabinae): description of five Nearctic species with phylogenetic considerations

Abstract

The larvae of five Nearctic species of Ilybiosoma Crotch, 1873, I. bjorkmanae (Hatch, 1939), I. lugens (LeConte, 1852), I. minnesotensis (Wallis, 1933), I. pandurus (Leech, 1942), and I. regularis (LeConte, 1852) are described for the first time including a detailed chaetotaxy analysis of the cephalic capsule, head appendages, legs, last abdominal segment and urogomphi. A provisional parsimony analysis based on 55 informative larval characteristics of 18 species in seven genera of the subfamily Agabinae was conducted using the program TNT. The larvae of the five Ilybiosoma species described were found to be fairly similar morphologically. Compared to the other species of Agabinae studied, larvae of Ilybiosoma stand out from most Agabini by the presence of the strongly emarginated siphon, which are reminiscent of the condition observed in Hydrotrupes Sharp, 1882 and Platynectes Régimbart, 1879.