|Crayfish often show high levels of morphological variation between and within populations. Studies have shown that environmental factors can play a role in determining external morphology. Increased levels of phenotypic variation can be advantageous for individuals in a novel environment. I used geometric morphometrics to determine the differences in the external morphology of introduced populations of Faxonius virilis over a broad spatial scale. I compared carapace morphology in populations collected from lentic and lotic habitats using geometric morphometric techniques. I found that crayfish from lotic habitats had more fusiform body shapes with greater relatively wide areola and that crayfish from lentic habitats had broader body shape with less relatively wide areola. To determine the effects of this variation in shape on the physiology of this species, I performed a respirometry study on individuals collected from an introduced population in Alabama. Using curves derived from 26 closed respirometry trials, Regulator Index scores were calculated to quantify the degree of regulation of respiratory rate. Following the respirometry trials, the carapace shapes of each crayfish was quantified using GMM techniques. I found that crayfish with conformatory strategies most often had a fusiform body shape, while crayfish with more regulatory strategies had a broader body shape. These body shapes correspond to the body shapes found in lotic and lentic crayfish, respectively.