Phylogenetic relationships of nearctic Colymbetinae (Coleoptera: Adephaga: Dytiscidae) based on chaetotaxic and porotaxic analysis of head capsule and appendages of larvae

An analysis of the primary setae and pores (campaniform sensilla) of first instars of 32 species of Colymbetinae, 61 species belonging to other dytiscid subfamilies, and seven species belonging to other families of Hydradephaga was performed to deduce the ancestral system of primary setae and pores of the head capsule and head appendages of Colymbetinae. Sixty-one setae and 46 pores have been assigned to the ground-plan pattern of the colymbetine larva, 27 setae and 20 pens on the head capsule and 34 setae and 26 pores on the cephalic appendages. The pattern proposed for the Colymbetinae is remarkably consistent and similar to the condition observed within the Carabidae. However, members of the Colymbetinae differ strongly from those of Hydroporinae which are characterized by several secondary losses. A pre preliminary phylogenetic reconstruction of the relationships of colymbetine genera studied based on 41 larval features suggests that the Nearctic fauna includes two monophyletic lineages: (1) (Agabus Leach + Ilybius Erichson) + Agabinus Crotch, and (2) {[Colymbetes Clairville + (Rhantus Dejean + Neoscutopterus Balfour-Browne)] + Matus Aube}.