Pseudosetia oblita (N. Tiberi, 1872)
Pusillina obscura (R.A. Philippi, 1844)
Turboella obsoleta (FOSSIL) (Wood, 1842 †)
Gofasia obtusellaeformis S. Gofas, 2007
Setia obtusispira G. Seguenza, 1876
Alvania occidua (B.C. Cotton, 1944)
Haurakia occulta (K.H.J. Thiele, 1925)
Alvania oceani (FOSSIL) d'Orbigny, 1852 †
Cingula ochroleuca Š. Brusina, 1869
Pusillina oenonensis (Š. Brusina, 1866)
Alvania ogasawarana (H.A. Pilsbry, 1904)
Rissoa olangoensis G.T. Poppe, S.P. Tagaro& P. Stahlschmidt, 2015
Alvania oldroydae P. Bartsch, 1911
Onoba oligochordata Güller & Zelaya, 2017
Benthonellania oligostigma P. Bouchet & A. Warén,1993
Onoba oliveri (A.W.B. Powell, 1955)
Alvania oliverioi G. Buzzurro, 2003
Onoba oliverioi C. Smriglio & P. Mariottini,2000
Haurakia onerata (FOSSIL) C.R. Laws, 1939 †
Rissoa ordinaria E.A. Smith, 1890
Attenuata orientalis (R.K. Dell, 1956)
Obtusella orisparvi (FOSSIL) Moreno, A. Peñas& E. Rolán, 2003 †
Lucidestea ornata (A.N. Golikov& O.V. Kussakin, 1967)
Crisilla orteai J. Templado & E. Rolán,1994
Pusillina otagoensis (R.K. Dell, 1956)
Cingula outis (J.R. le B. Tomlin, 1931)
Onoba ovata (K.H.J. Thiele, 1912)
Manzonia overdiepi J.J. Van Aartsen, 1983
Crisilla ovulum S. Gofas, 2007
Botryphallus ovummuscae (S. Gofas, 1990)
Alvania paatsi H.J. Hoenselaar & J. Goud,1998
Merelina pagodiformis (G.B. III Sowerby, 1914)
Alvania pagodula M.E.J. Bucquoy & al.,1884
Lucidestea pallaryi (A. Hornung & G. Mermod,1927)
Onoba palmeri (W.H. Dall, 1919)