A molecular phylogenetic analysis based on gene fragments of the first subunit of the mitochondrial cytochrome-c-oxidase (COI) from Siberian glossiphoniids and phylogenetically relative Palearctic species demonstrated that Siberian representatives do not belong to the species Glossiphonia complanata, as was believed previously, and have an autonomous taxonomic status. Furthermore, the detected genetic distances make it possible to accept the mtCOI fragment as a suitable marker for the molecular identification of the species within the Glossiphoniidae (Hirudinea).