Oceanapia jeffreysii – synonym of Oceanapia robusta
Oligoceras collectrix – synonym of Hyrtios collectrix
Ophlitaspongia basifixa – synonym of Clathria basifixa
Ophlitaspongia papilla – synonym of Clathria seriata
Ophlitaspongia seriata – synonym of Clathria seriata
Orina angulata – synonym of Haliclona angulata
Orina consimilis – synonym of Hemigellius arcoferus
Oxeostilon annandalei – synonym of Spongosorites annandalei