A description and functional interpretation of the mandibular geometry of Agabus punctatus Melsheimer, 1844, Rhantus calidus (Fabricius, 1792) and Acilius mediatus (Say, 1823), (Coleoptera: Dytiscidae)

Abstract

Eleven morphometric, geometric, and/or biomechanical parameters are developed and presented as quantitative descriptors of dytiscid mandibles. These include arc, angle of attack, maximum camber, position of maximum camber, basal angle, and abductor and adductor gear ratios. This quantifiable character set distinguishes mandibles of Acilius from those of Agabus and Rhantus, a likely indication of exploitation of an open water prey regime by larvae of Acilius. Components of this prey regime are probably encountered only rarely by larvae of A. punctatus, and R. calidus. The comparison of A. punctatus, and R. calidus also revealed significant differences between mandibles of these two species with respect to proportional length, arc, angle of attack, and maximum camber. These differences suggest that the prey regimes exploited in situ by larvae of each of these two also includes different prey species.