Sperm ultrastructure in two species of Choanomphalus (Hygrophila: Lymnaeoidea: Planorbidae).

Sperm ultrastructure has been successfully used in gastropod taxonomy and here we attempted to identify potential synapomorphies within the Hygrophila, a group of freshwater lung-bearing gastropods, by examining sperm morphology and ultrastructure in two hygrophilan species of the genus Choanomphalus Gerstfeldt, 1859 (Lymnaeoidea: Planorbidae): Ch. riparius (Westerlund, 1865) and Ch. rossmaessleri (A.