Phylogenetic relationships among the four currently recognized species in the genus (Erimyzon) were reconstructed using sequence data obtained from the mitochondrially encoded COI and the nuclear-encoded IRBP2 genes. Maximum likelihood and Bayesian analyses yielded five groups of (Erimyzon). Three of the clades corresponded to the species (E. oblongus), (E. tenuis), and (E. claviformis). Individuals identified as (E. sucetta) were split into two separate clades, with one clade more closely related to (E. oblongus) than to the other (E. sucetta) clade in three of four analyses. Two instances of putative hybridization between sympatrically distributed species were also detected, one involoving (E. oblongus) and (E. sucetta) and the other involving (E. claviformis) and (E. tenuis) The results suggest that the currently recognized (E. sucetta) comprises two species, with potentially non-overlapping distributions. Further morphological investigation is warranted to provide additional support for recognizing this putative fifth species of (Erimyzon).