• Octocanna funeraria
• Octopus vulgaris
• Ocypode ceratophthalma Sand crab
  Tsunome-gani
  
• Ocypode cordimanus Minami-sunagani
  
• Ocypode mortoni Muroto-sunagani
  
• Ocypode sinensis Chugoku-sunagani
  
• Ocypode stimpsoni Sunagani
  
• Odhneria acutidens Odhner-samehada-ohgigani
  
• Odhneria echinus Togesamehada-ohgigani
  
• Oikopleura dioica
• Oikopleura fusiformis
• Oikopleura labradoriensis
• Oikopleura parva
• Oikopleura vanhoeffeni
• Ommastrephes bartramii
• Ommatocarcinus fibriophthalmus Hime-menaga-énkougani
  
• Ommatocarcinus macgillivrayi Menaga-énkougani
  
• Ommatocarcinus pulcher Natal-menaga-énkougani
  
• Oncinopus angustifrons Higashi-shinakai-kumogani
  
• Oncinopus aranea Kumogani
  
• Oncinopus neptunus Mindro-ákeúsu
  
• Onychoteuthis banksii
• Opecarcinus crescentus Ana-sango-yadori-gani
  
• Oregonia gracilis Graceful decorator crab
  Kesengani
  
• Oregonia mutsuensis Mutsu-kesengani
  
• Oreotlos havelocki Menko-kobushi
  
• Oreotlos heuretos Tanng-karuishi-gani
  
• Oreotlos latus Maldive-karuishi-gani
  
• Orientotlos iishibai Toyo-ébaria
  
• Orithyia sinica Kitou-gani
  
• Orthoconchoecia haddoni
• Orthopyxis integra
• Orthotheres turboe Sazae-pinno
  
• Osachila expansa Osachila-hishigani
  
• Ostracotheres subquadratus Tsumenashi-pinno
  
• Ovalipes iridescens Hime-hira-tsumegani
  
• Ovalipes punctatus Three-spot swimming crab
  Hira-tsumegani
  
• Oxypleurodon bidens Futaba-íbogani
  
• Oxypleurodon nodosus Kobu-íbogani
  
• Oxypleurodon stimpsoni Ibogani
  
• Oxypleurodon velutinus Mimitsuki-tsunogani
  
• Ozius guttatus Ohíso-ohgigani
  
• Ozius rugulosus Iso-ohgigani
  
• Ozius tuberculosus Tsubu-íso-ohgigani
  
• Pachygrapsus crassipes Lined shore crab
  Iwagani
  
• Pachygrapsus fakaravensis Kosuji-ìwagani
  
• Pachygrapsus marinus Taiyou-ìwagani
  
• Pachygrapsus minutus Hime-ìwagani
  
• Pachygrapsus plicatus Ko-ìwagani
  
• Paeduma orientale Asia-mutsuashi-gani