Obelia, Genus
Obeliinae, Subfamilia
Obtusoecia, Genus
Octocanna, Genus
Octopoda, Ordo
Octopodidae, Familia
Octopodinae, Subfamilia
Octopus, Genus
Oegopsida, Subordo
Oikopleura, Genus
Oikopleuridae, Familia
Olindiasidae, Familia
Ommastrephes, Genus
Ommastrephidae, Familia
Ommastrephinae, Subfamilia
Onychoteuthidae, Familia
Onychoteuthis, Genus
Ophiuroidea, Classis
Opisthobranchia, Subclassis
Opistobranchia, Subclassis
Oplophoridae, Familia
Orthoconchoecia, Genus
Orthopyxis, Genus
Ostracoda, Subclassis