 The overall outline of the shell is still used for species identification in recent malacological literature.Though the coloration and patterns of the shells cannot be relied upon to identify specimens, opercular characters can be used for a proper identification of "Theodoxus fluviatilis".The calcified operculum of "T. fluviatilis" is D-shaped, light reddish with a red margin, bearing a broad rib (also called a ridge) on its inner surface.