Anisus nummulus (F. Held, 1837)
Gyraulus nusici (P.S. Pavlovic, 1903)
Bulinus nyassanus E.A. Smith, 1877
Africanogyrus oasiensis (E.S. Demian, 1962)
Amerianna obesula T. Iredale, 1943
Bathyomphalus obesus (FOSSIL) (J.L.Jr. Baily, 1858 †)
Anisancylus obliquus (W.J. Broderip& G.B. I Sowerby, 1832)
Biomphalaria obstructa (P.M.A. Morelet, 1849)
Ancylastrum obtusata B. Walker, 1926
Bulinus obtusispira E.A. Smith, 1882
Bulinus obtusus G. Mandahl-Barth, 1973
Planorbella occidentalis J.G. Cooper, 1870
Biomphalaria occidentalis W.L. Paraense, 1981
Glyptophysa oconnori (R.A. Cumber, 1941)
Bulinus octaploidus J.B. Burch, 1972
Gyraulus oecsensis W.A. Wenz, 1919
Segmentina oelandica (C.A. Westerlund, 1885)
Choanomphalus okhoticus L.A. Prozorova& Y.I. Starobogatov, 1997
Gyraulus okrugljakensis T.A. Neubauer & al., 2014
Biomphalaria oligoza W.L. Paraense, 1975
Anisus omalus (FOSSIL) (J.R. Bourguignat,1881 †)
Choanomphalus omphalotus W. Dybowski, 1901
Gyraulus oncostomus (Š. Brusina, 1902)
Menetus opercularis (A.A. Gould, 1847)
Gyraulus orahovacensis (P.S. Pavlovic, 1903)
Biomphalaria orbicula (P.M.A. Morelet, 1849)
Ancylus orbicularis F. Held, 1837
Biomphalaria orbignyi W.L. Paraense, 1975
Planorbella oregonensis G.W. Tryon, 1865
Physastra ovalina (E.C. Von Martens, 1897)
Physopsis ovoidea J.R. Bourguignat, 1879
Gyraulus oxystoma (E. Klein, 1846 )
Gyraulus pachychilus (Š. Brusina, 1902)
Ferrissia pallaryi B. Walker, 1914
Biomphalaria pallidus (C.B. Adams, 1848)