Lithoglyphus prasinus (Küster, 1852) is the only representative of the genus Lithoglyphus which, instead of rivers, inhabits oligostenothermal waters of karst springs. The taxon is probably endemic to central and southeastern Slovenia and the adjacent territories of Croatia. Apart from the ecology and shell morphology, there are no differences between L. prasinus and the other Lithoglyphus species. The species distinctness of the taxon is doubtful; it has been postulated to be an oligostenothermal ecotype or race of L. naticoides. In the present paper partial sequences of cytochrome oxidase subunit I (COI) of mtDNA were used to check the species distinctness of L. prasinus from the Moèilnik spring of Ljubljanica river in Slovenia. For the COI sequences K2P distances between the two taxa were 0.03170-0.03347. This, coupled with small intraspecific differences in both taxa, suggests that L. prasinus is a distinct species.