Caspia is an endemic Ponto-Caspian Basin genus of hydrobiid gastropods. Around a dozen nominal species of Caspia have been described to inhabit the Caspian Sea while four species occupy a restricted zone in the lower part of the rivers flowing into the Black Sea and the Sea of Azov. Scanning electron microscopic study of the protoconch and radula morphology of two Caspia species from the Azov–Black Sea Basin allows re-evaluation of the taxonomic rank and attribution of the genus. The adult shell geometry and characters of ornamentation do not enable clear demarcation of these species of Caspia but the protoconch parameters do allow their differentiation. Available morphological data on Caspia and the related genus Caspiohydrobia are interpreted here as confirmation of the subfamilial rank of Caspiinae in the family Hydrobiidae, in contrast to the previous affiliation of this group with Pyrgulidae.