The sutural margins of the elytra of adult beetles are in the form of a ‘tongue and groove’ joint and are bilaterally asymmetrical. Species in Haliplidae have unequal numbers of individuals with the tongue on the left (sinistral) and right (dextral) elytron. This implies that the direction of asymmetry is inherited even though the asymmetry appears to be generated when the teneral adult first closes its elytra. The species in Brychius Thomson and Peltodytes Régimbart include predominantly sinistral individuals. Haliplus Latreille contains two groups: a sinistral group including the species in the subgenera Haliplus s.str., Neohaliplus Netolitzky and probably Haliplidius Guignot plus H. (Liaphlus) laminatus (Schaller) and H. (Paraliaphlus) borealis LeConte; and a dextral group including the remaining species in the subgenera Liaphlus Guignot and Paraliaphlus Guignot. These results support splitting Haliplus into two genera and the reassignment of H. laminatus and H. borealis to Haliplus s.str. Species from nine other families were examined as out-groups; hydradephagan species are dominantly dextral while most geadephagan species are antisymmetric, including equal numbers of sinistral and dextral individuals.