On the phylogenetic positioning of the South American freshwater crayfish genera (Decapoda : Parastacidae)

South America contains three endemic genera of parastacid freshwater crayfi shes (i.e., Parastacus Huxley, Samastacus Riek, and Virilastacus Hobbs), wi th a current total of ten described species. A previous author has argued t hat each of these genera has closer affinities with genera from Australia t han to each other. We sequenced approximately 500 nucleotides of the 16S ge ne from mitochondrial DNA to estimate phylogenetic relationships among the South American genera of freshwater crayfishes and determined their phyloge netic positioning relative to the Australian genera. We sampled seven speci es representing all three genera from South America with 19 individuals. Th ese sequences were combined with other Australasian crayfishes for a total representation of 54 sequences covering 13 genera. Our results indicate tha t the South American genera form a well-supported monophyletic group closel y related to a subset of the Australasian crayfishes (Paranephrops and Para stacoides). Our results also provide strong support for the currently recog nized generic designations.