Decapod crustaceans bearing major claws with long, slender fingers armed with pectinate (comblike) denticles have been described in six genera arrayed within three families (Polychelidae, Nephropidae, and Ctenochelidae) in three infraorders (Palinura, Astacidea, and Anomura, respectively). Only one or a few genera in each infraorder exhibit this claw form. The pectinate claw form is confidently interpreted as having evolved independently in four lineages: once in the Polychelidae, once in the Ctenochelidae, and twice in the Nephropidae. Three of the lineages are known from both the fossil record and modern seas; the polychelid form is known only from Jurassic rocks. Convergence in this claw form developed to the extent that isolated fossil claws (i.e., claws without associated bodies) have commonly been misidentified at high taxonomic levels. The fossil record confirms what seems intuitively reasonable: that claw morphology is prone to convergence and should not, by itself, be given a high degree of taxonomic importance.

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