The phylogeny of freshwater crayfish, including both fossil and extant taxa, is assessed using morphologic analysis and nucleotide sequencing. Based on external morphologic characters, primarily characters of the carapace and appendages, the crayfish are reconfirmed as a monophyletic group. The nearest sister taxon to the crayfish is the Chilenophoberidae. Within the crayfish, the longstanding distribution of species among three families is supported. The superfamily Astacoidea is redefined to include three families, Astacidae, Cambaridae, and Parastacidae. By including the Parastacidae in the Astacoidea, the superfamily Parastacoidea becomes superfluous and is now suppressed. The Astacoidea is characterized by several synapomorphies: a diaresis of the telson, mobility of the last thoracic segment, and carapace groove pattern. Species in the Parastacidae are characterized by change in calcification of the telson. Species in the Cambaridae are characterized by the apomorphous annulus ventralis in the female and hooks on the ichiopodites of one or more pereiopods in the male. Species in the Astacidae are characterized by an apomorphous medial rostral ridge. Nucleotide sequencing (18s and 16s ribosomal mtDNA) of extant crayfish species supports the phylogenetic pattern inferred from character analysis.No embarg
