Systematics of adult lampreys based on the “paired species” concept divides anadromous and residential specimens mostly on the size and size-depended criteria. Larvae of the paired species are poorly distinguished, so scientists keep looking for new diagnostic features. In the present paper structure and coloration of the tongue precursor in Arctic lamprey, Lethenteron camtschaticum, from the watersheds of the Russian Far East, including the species type locality are discussed. The data show that use of Tongue Precursor Pigmentation as a key for species identification is premature because tongue precursor within species inhabiting one river system or the same region demonstrates all types of coloration. Structure of tongue precursor changes from triangular into bulbous during growth.