Cornigerius species are endemic to the Ponto-Caspian, with the exception of Cornigerius lacustris, which is endemic to freshwater Lake Hazar in the Euphrates basin. However, the barcoding fragment of the cytochrome c subunit I (COI) of animals from the type locality shows less than 1 % divergence with Black Sea and less than 2% with Caspian Lake C. maeoticus, the oldest and most widespread species of the genus. Black Sea and Caspian Lake animals show 1.5 % divergence. We therefore place the origin of the Hazar population in the Black Sea. Combined with a variable morphology, we also conclude that C. lacustris is a synonym of C. maeoticus, as already suspected by its describer. Dating the 'lacustris' population is difficult, but it has been there for at least a century.