Blue-ringed octopi, comprising the genus Hapalochlaena, are four highly venomous species of octopus that are found in tide pools and coral reefs in the Pacific and Indian oceans, from Japan to Australia. They can be identified by their yellowish skin and characteristic blue and black rings that change color dramatically when the animal is threatened. They eat small crustaceans, including crabs, hermit crabs, shrimp, and other small sea animals.
They are one of the world's most venomous marine animals. Despite their small size—12 to 20 cm (5 to 8 in)—and relatively docile nature, they are very dangerous to humans if provoked when handled because their venom contains the powerful neurotoxin tetrodotoxin.
The species tend to have a lifespan of approximately two to three years. This may vary depending on factors such as nutrition, temperature and the intensity of light within its habitat.