The genetic variation of the copepod Chondracanthus psetti, ectoparasite of the small-eyed flatfish Paralichthys microps was, investigated by horizontal starch gel electrophoresis. Nine enzymatic systems with thirteen loci were tested. Four had equal electrophoretic mobility, and nine had differences significant enough to be considered diagnostic loci to separate copepods into two different groups. Based on this genetic differentiation, we report that two species are included within the copepod C. psetti. The importance of differential microhabitat utilization in the speciation process of both morphs of C. psetti found is discussed.