The recently explored Cueva de Los Camarones, in the remote village of Constitucion, Chiapas, Mexico, houses a unique highly variable population of Procambarus crayfish (Crustacea, Decapoda). Morphologically, a more or less clinal variation is revealed at several features such as the degree of rudimentation in both pigmentation and eye, and the elongation of body and appendages. Extremes are quite different, ranging from typical dark, thick, eyed individuals to light, elongated, microphtalmic phenotypes. Evolutionary relationships among individuals were investigated electrophoretically (25 structural gene loci) and morphometrically (12 characters) by means of multivariate analyses. Results from analysis of individual allozymic multilocus profiles indicate that the “light” phenotypes belong to a distinct gene pool with respect to the “dark” ones, but some level of introgression is hypothesized. Results from analysis of individual morphometric profiles also show a discrimination between "light" and "dark" samples, chiefly determined by the shape of the rostrum and chela. The existence of such a discontinuous variation both in morphometric and allozymic characters presumably reflects a history of allopatric divergence followed by secondary contact of the two species.