 "Theodoxus fluviatilis" can be distinguished from the other three mentioned species by having a rib pit, which is formed by the rib and the rib shield.The rib shield, and consequently a rib pit, are lacking in "Theodoxus transversalis", "Theodoxus danubialis" and "Theodoxus prevostianus".These three species differs in having, in addition to a rib, a peg, which is absent in "T. fluviatilis".