Obesula mamillata (nippled sinistral-creeper)

Obrussena bracteata (plated acteon)

Octopoteuthis rugosa (rough squid)

Octopus berrima (southern keeled octopus)

Octopus bunurong (southern white-spot octopus)

Octopus kaurna (southern sand octopus)

Octopus maorum (Maori octopus)

Octopus pallidus (pale octopus)

Octopus superciliosus (frilled pygmy octopus)

Octopus tetricus (gloomy octopus)

Octopus warringa (club pygmy octopus)

Ocythoe tuberculata (football octopus)

Odostomia crassicosta (thick-ribbed pyramid-shell)

Odostomia deplexa (unwoven pyramid-shell)

Odostomia diaphana (transparent pyramid-shell)

Odostomia mayii (May’s pyramid-shell)

Odostomia micra (tiny pyramid-shell)

Odostomia occultidens (hidden-toothed pyramid-shell)

Odostomia tasmanica (Tasmania pyramid-shell)

Okenia BURN sp 01 (BURN sp 01 okenia sea-slug)

Okenia mija (daughter sea-slug)

Ollaphon molorthus (sounding-lead trophon)

Ommastrephes bartramii (Bartram’s squid)

Onchidella nigricans (limpet-like sea-slug)

Onchidoris maugeansis (Mauge’s sea-slug)

Onoba agnewi (Agnew’s rice-shell)

Onoba australiae (Australian rice-shell)

Onoba demessa (mown rice-shell)

Onoba freycineti (Freycinet’s rice-shell)

Onoba multilirata (many-grooved rice-shell)

Onoba perpolita (well-polished rice-shell)

Onoba pertumidus (swollen rice-shell)

Onoba puer (Point Puer rice-shell)

Onoba rubicunda (ruddy rice-shell)

Onoba supracostata (ribbed rice-shell)

Onoba tiara (tiara rice-shell)

Onychoteuthis banksii (Bansk’s squid)

Oocorys sulcata (furrowed false-tun)

Opalia australis (southern wentletrap)

Opalia granosa (grainy wentletrap)

Ophicardelus ornatus (mangrove air-breather)

Opisthoteuthis persephone (persephone octopus)

Opisthoteuthis pluto (pluto octopus)

Orbitestella iredalei (Iredale’s orbitestellid)

Orbitestella mayi (May’s orbitestellid)

Ostrea angasi (common mud-oyster)

Ovacuna atkinsoni (Atkinson’s condyl-clam)

Ovaginella ovulum (egg margin-shell)

Oxynoe viridis (bright-green sea-slug)