Stilapex okadai T. Habe, 1986
Melanella oleacea (J.D. Kurtz & W. Stimpson,1851)
Entocolax olgae Nekhaev, 2016
Melanella olssoni P. Bartsch, 1924
Megadenus oneirophantae P. Bouchet & C.F. Lützen,1980
Melanella opaca (G.B. II Sowerby, 1865)
Melanella opalina (L. de Folin, 1867)
Melanella opalina (W.B. Marshall, 1901)
Hemiliostraca ophiarachnicola H. Matsuda, D. Uyeno& K. Nagasawa, 2013
Fuscapex ophioacanthicola A. Warén, 1981
Melanella ophiodon W.H. Dall, 1927
Punctifera ophiomoerae A. Warén, 1981
Mucronalia ophiuraphila T. Habe, 1974
Sabinella orbignyana (L.H. Hupé, 1860)
Molpadicola orientalis Grusov, 1957
Melanella orphanensis A.H. Clarke, 1974
Hypermastus orstomi A. Warén, 1994
Melanella orthophyes (R. Sturany, 1903)
Subniso osorioae (B.K. Raines, 2003)
Melanella otagoensis (A.W.B. Powell, 1927)
Margineulima otaioensis (FOSSIL) (C.R. Laws, 1933 †)
Curveulima otakauica (R.K. Dell, 1956)
Oceanida ovalis L. de Folin, 1884
Apicalia ovata (W.H. Pease, 1860)
Echineulima ovata (W.H. Pease, 1861)
Stilifer ovoideus H. Adams & A. Adams, 1853
Melanella oxyacme (H.H. Suter, 1908)
Melanella oxytata (R.B. Watson, 1883)
Mucronalia oxytenes J.C. Melvill, 1904
Eulima ozawai M. Yokoyama, 1927
Sabinella pachya (P. Dautzenberg& H. Fischer, 1896)
Eulima pachychila O. Böttger, 1893
Eulima padangensis (K.H.J. Thiele, 1925)
Eulimetta pagoda A. Warén, 1992
Pyramidelloides pagoda (A.W.B. Powell, 1926)