Blue-ringed octopuses, comprising the genus Hapalochlaena, are four extremely 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 can change color dramatically when the animals are threatened. They eat small crustaceans, including crabs, hermit crabs, shrimp, and other small sea animals.

They are some 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 if provoked when handled because their venom contains a powerful neurotoxin called tetrodotoxin.

The species tends to have a lifespan around two to three years, which may vary depending on factors such as nutrition, temperature, and the intensity of light within its environment.