David Fleetham / Day / Big blue octopus (Octopus cyanea) with diver in background. Hawaii. September 2012.

David Fleetham / Day / Common Reef Octopus (Octopus cyanea) swimming. Hawaii.

David Fleetham / Common reef octopus (Octopus cyanea), Hawaii.

Alex Mustard / Reef octopus (Octopus cyanea) portrait near wreck. Gubal Island, Egypt. Red Sea.

Alex Mustard / Pacific giant octopus (Enteroctopus dofleini) hunts for food on a colourful reef in Browning Pass, Vancouver Island, British Columbia, Canada

Georgette Douwma / Common reef / Day octopus hunting for crustaceans and fish, enclosing coral head with arms and webs, using the arm tips to flush out prey into waiting suckers {Octopus cyaneus} Andaman Sea, Thailand

Georgette Douwma / Common reef / Day octopus {Octopus cyaneus} at rest on coral reef Sipadan, Malaysia

David Hall / Day octopus (Octopus cyanea) jetting over coral reef. Komodo, Indonesia.

Magnus Lundgren / Wild Wonders of China / Big blue octopus (Octopus cyanea) , Xiaoliuqiu Island, Taiwan

Magnus Lundgren / Wild Wonders of China / Big blue octopus (Octopus cyanea) close up of eye Xiaoliuqiu Island, Taiwan

Gary Bell/ Oceanwide / Reef Octopus (Octopus cyanea) pair, Milne bay, Papua New Guinea

Gary Bell/ Oceanwide / Reef Octopus (Octopus cyanea), Milne Bay, Papua New Guinea