astacidae, cambaridae, cambaroididae, crustacea, decapoda, parastacida

Mandibles of representatives of the Holarctic crayfish families Astacidae, Cambaridae,and Cambaroididae were examined using SEM, and the results were analyzed in a phy-logenetic framework. The intraspecific variability of the incisor process was found tobe higher than its interspecific variability, mainly due to extensive abrasion of its ridgeduring intermolt periods. The plesiomorphic state of the crayfish mandibles highlightsthe dentate–crenate type of the incisor process and the extensive ribbed molar fieldwith a multicuspidate caudal part, typical of the two parastacid crayfish examined forcomparison. For Holarctic crayfish, the initial evolutionary type of the incisor is alsothe dentate–crenate one, but the molar field has a bowl-shaped caudal part andreduced cephalic part, both of which have been shown, for example, forCambaroides.Similar mandibles are also widely present in American cambarids, which furtherevolved a blade-like incisor process (someFaxoniusspp.) or a tricuspidate or double-bladed caudal molar field(someProcambarusspp.). The molar field in Astacidae crayfishis subdivided and rugose. The results of the present study indicate that little phyloge-netic information is conveyed by the mandible shape at the species or genus level. Evo-lutionary changes are indicated mainly on the level of the main crayfish families