Pyrgulopsis notidicola R. Hershler, 1998
Goniochilus novakovici (FOSSIL) Š. Brusina, 1902 †
Belgrandiella novoselensis P. Radoman, 1975
Horatia novoselensis P. Radoman, 1966
Micromelania nuda (FOSSIL) E. Jekelius, 1932 †
Phreatodrobia nugax (H.A. Pilsbry& J.H. Ferriss, 1906)
Pseudamnicola numidica (S. Clessin, 1878)
Pyrgulopsis nuwuvi Hershler, Liu, Forsythe, Hovingh& Wheeler, 2017
Pseudamnicola nympha (FOSSIL) (K.E.I. von Eichwald,1853 †)
Peringia obeliscus (A. Paladilhe, 1869)
Bania obliquaecostata (FOSSIL) T.A. Neubauer & al.,2013 †
Prososthenia oblonga (FOSSIL) (H.G. Bronn, 1831 †)
Micromelania obradovici (FOSSIL) Š. Brusina, 1902 †
Caspiohydrobia obrutchevi Y.I. Starobogatov& S.I. Andreeva, 1981
Hydrobia obtusa (FOSSIL) C.L.F. von Sandberger,1849 †
Caspia obtusa (FOSSIL) Š. Brusina, 1892 †
Staja obtusecarinata (FOSSIL) (A. Fuchs, 1870 †)
Belgrandiella ocalis H.D. Boeters, 2008
Pseudohoratia ochridana (W. Polinski, 1929)
Hydrobia octona (J.G. Bruguière, 1792)
Nematurella oepfingensis (FOSSIL) W.A. Wenz, 1918 †
Marstonia ogmorhaphe T.E. Thompson, 1977
Gocea ohridana S. Hadžišce, 1956
Strugia ohridana P. Radoman, 1973
Pyrgulopsis ojaiensis R. Hershler,H.X. Liu & al., 2016
Marstonia olivacea (H.A. Pilsbry, 1895)
Alzoniella onatensis H.D. Boeters, 2003
Hydrobia onuri (FOSSIL) Taner, 1974 †
Subtilistriata operculomphalus (FOSSIL) Pan, 1980 †
Yongkangia opima (FOSSIL) Yü, 1980 †
Austropyrgus ora A. Clark, W.B. Miller& W.F. Ponder, 2003
Pyrgulopsis orbiculata R. Hershler, 1998
Akiyoshia orientalis Kabe, 1986
Pseudamnicola orientalis (FOSSIL) (Bukowski, 1896 †)
Micromelania orientalis (FOSSIL) Willmann, 1981 †