Differentiation of selected species of Belgrandiella and the redefined genus Graziana (Gastropoda: Hydrobiidae)

Seven species of the genus Belgrandiella A. J. Wagner, 1928 ( sensu lato ), from Austria and Italy are described in detail. The genus Graziana Radoman, 1975, is redefined on a newly discovered character of the stomach, the shield caecum. This is remarkable, since hydrobiid genera are usually defined by characters of the reproductive system. Two species, B. pelerei sp. nov. and G. klagenfurtensis sp. nov. , are new to science. Allozyme electrophoresis of ten populations of these seven species revealed an unusual lack of variability within each population. This is explained as a consequence of the presumed mode of dispersal of these crenobiontic snails, i.e. aerial transport with insects. Genetic distances between conspecific populations and congeneric species fall within the expected range. The only exception is the genetic identity of G. klagenfurtensis and G. lacheineri Küster, 1853. This identity is probably due to the recent origin of G. klagenfurtensis , whose area was covered with ice during the Wtirm glaciation. The high distance values between Belgrandiella and Graziana justify the generic separation based on a character of the digestive system. This is also confirmed through the comparison with three species of the genus Hydrobia Hartmann, 1821, which differs in all systematically relevant aspects from the other two genera.