Anisus nummulus (F. Held, 1837)
Gyraulus nusici (P.S. Pavlovic, 1903)
Bulinus nyassanus E.A. Smith, 1877 Mozambique, Lake Malawi
Africanogyrus oasiensis (E.S. Demian, 1962) Egypt
Amerianna obesula T. Iredale, 1943 Australia
Bathyomphalus obesus (FOSSIL) (J.L.Jr. Baily, 1858 †)
Anisancylus obliquus (W.J. Broderip& G.B. I Sowerby, 1832) Uruguay, Colonia
Biomphalaria obstructa (P.M.A. Morelet, 1849) Florida, Jacksonville11 mm
Ancylastrum obtusata B. Walker, 1926 South Africa
Bulinus obtusispira E.A. Smith, 1882 Madagascar
Bulinus obtusus G. Mandahl-Barth, 1973 Chad
Planorbella occidentalis J.G. Cooper, 1870 California, Santa Cruz
Biomphalaria occidentalis W.L. Paraense, 1981 Colombia13,9 mm
Glyptophysa oconnori (R.A. Cumber, 1941) New Zealand
Bulinus octaploidus J.B. Burch, 1972 Ethiopia
Gyraulus oecsensis W.A. Wenz, 1919
Segmentina oelandica (C.A. Westerlund, 1885) Sweden, Öland Island
Choanomphalus okhoticus L.A. Prozorova& Y.I. Starobogatov, 1997
Gyraulus okrugljakensis T.A. Neubauer & al., 2014
Biomphalaria oligoza W.L. Paraense, 1975 Brazil
Anisus omalus (FOSSIL) (J.R. Bourguignat,1881 †)
Choanomphalus omphalotus W. Dybowski, 1901
Gyraulus oncostomus (Š. Brusina, 1902)
Menetus opercularis (A.A. Gould, 1847) Washington, Seattle
Gyraulus orahovacensis (P.S. Pavlovic, 1903)
Biomphalaria orbicula (P.M.A. Morelet, 1849) Mexico, Yucatan
Ancylus orbicularis F. Held, 1837
Biomphalaria orbignyi W.L. Paraense, 1975
Planorbella oregonensis G.W. Tryon, 1865 Oregon
Physastra ovalina (E.C. Von Martens, 1897)
Physopsis ovoidea J.R. Bourguignat, 1879 Tanzania14,1 mm
Gyraulus oxystoma (E. Klein, 1846 )
Gyraulus pachychilus (Š. Brusina, 1902)
Ferrissia pallaryi B. Walker, 1914 Egypt
Biomphalaria pallidus (C.B. Adams, 1848) Jamaica