Re-descriptions of larvae of Hoperius and Meladema and phylogenetic implications for the tribe Colymbetini (Coleoptera Dytiscidae)

New descriptions of the larvae of Meladema lanio (Fabricius), M. coriacea Laporte and Hoperius planatus Fall are provided. Characters from larval morphology are analyzed to infer the phylogenetic relationships of the genera Meladema Laporte and Hoperius Fall with other genera of the tribe Colymbetini (Colymbetinae). Larvae of Meladema are unique among other Colymbetini being characterized by the presence of a variable number of additional setae along the dorsal margin of both femora and tibiae. Larvae of Hoperius reveal to be remarkably modified and autapomorphic being characterized by a short antennomere II, the presence of a variable number of secondary setae on antennomeres I - II and maxillary palpomere, an elongate maxillary palpus, and a narrow and elongate mandible. A parsimony analysis based on 30 informative larval characters is carried out. Whereas the 12 most parsimonious trees support the placement of Meladema as sister to Neoscutopterus J. Balfour-Browne, the relative position of Hoperius remains unresolved within the Colymbetini. Larvae of Meladema share with those of Neoscutopterus: (i) the presence of additional setae both on the frontoclypeus and parietale, (ii) the presence of a large number of secondary setae on trochantera, (iii) the absence of spinulae along ventral margin of mesotibia and mesotarsus and (iv) the presence of additional setae both on abdominal segment VIII.