Claim: One of the marine animals that is the most venomous is the blue-ringed octopus.

The blue-ringed octopodes -LRB- genus Hapalochlaena -RRB- are three octopus species that live in tide pools and coral reefs in the Pacific and Indian Oceans , from Japan to Australia . Their primary habitat is around southern New South Wales , South Australia , and northern Western Australia . They are recognized as one of the world 's most venomous marine animals . Despite their small size , 12 to , and relatively docile nature , they are dangerous to humans if provoked and handled , because their venom contains tetrodotoxin , a neurotoxin powerful enough to kill humans .   They can be identified by their characteristic blue and black rings , and yellowish skin . When the octopus is agitated , the brown patches darken dramatically , iridescent blue rings , or clumps of rings , appear and pulsate within the maculae . Typically , 50 -- 60 blue rings cover the dorsal and lateral surfaces of the mantle .   They hunt small crabs , hermit crabs , shrimp , and other small crustaceans .