Sexual dimorphism in the chela of Orconectes virilis (Hagen)

The length and width of the left and right chela and the carapace length of 67 mature crayfish were measured to [Formula: see text]. The regression lines for the carapace length vs. chela length showed a measurable difference in chela length for the three adult groups. Form I male chela were found to be 19% longer and 12% wider than the form II male chela and 24% longer and 16% wider than the female chela. The form II male chela were 8% longer and 5% wider than the female chela. The ratio of chela length to chela width showed that the chela of all the three groups had slightly different shapes.