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 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——and relatively docile nature, they are very dangerous to humans if provoked when handled because their venom contains a powerful neurotoxin called tetrodotoxin.
The species tends 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 environment.
Classification
The genus was described by British zoologist Guy Coburn Robson in 1929. There are four confirmed species of Hapalochlaena, and six possible but still undescribed species being researched: Greater blue-ringed octopus (Hapalochlaena lunulata) Southern blue-ringed octopus or lesser blue-ringed octopus (Hapalochlaena maculosa) Blue-lined octopus (Hapalochlaena fasciata) Hapalochlaena nierstraszi was documented and described in 1938 from a single specimen found in the Bay of Bengal, with a second specimen caught and described in 2013.
Behavior
Blue-ringed octopuses spend most of their time hiding in crevices while displaying effective camouflage patterns with their dermal chromatophore cells. Like all octopuses, they can change shape easily, which allows them to squeeze into crevices much smaller than themselves. This, along with piling up rocks outside the entrance to its lair, helps safeguard the octopus from predators.
If they are provoked, they quickly change color, becoming bright yellow with each of the 50–60 rings flashing bright iridescent blue within a third of a second as an aposematic warning display. In the greater blue-ringed octopus (Hapalochlaena lunulata), the rings contain multi-layer light reflectors called iridophores. These are arranged to reflect blue–green light in a wide viewing direction. Beneath and around each ring are dark pigmented chromatophores which can be expanded within 1 second to enhance the contrast of the rings. There are no chromatophores above the ring, which is unusual for cephalopods as they typically use chromatophores to cover or spectrally modify iridescence. The fast flashes of the blue rings are achieved by using muscles which are under neural control. Under normal circumstances, each ring is hidden by contraction of muscles above the iridophores. When these relax and muscles outside the ring contract, the iridescence is exposed, thereby revealing the blue color.
Similar to other Octopoda, the blue-ringed octopus swims by expelling water from a funnel in a form of jet propulsion.
Feeding
The blue-ringed octopus often feeds on fish and crustaceans. It pounces on its prey, seizing it with its arms and pulling it towards its mouth. It uses its horny beak to pierce through the tough crab or shrimp exoskeleton, releasing its venom. The venom paralyzes the muscles required for movement, which effectively kills the prey. The octopus is yellow with dark brown rings while it is at rest, but when agitated, the rings turn into vivid blue. The chromatophores, an assortment of elastic ink-filled sacs found beneath the skin, are responsible for this shift in ink color. When the octopus feels threatened, the chromatophores stretch and the animal's rings turn a bright neon blue. The sac will contract as soon as the danger has passed.
Reproduction
The mating ritual for the blue-ringed octopus begins when a male approaches a female and begins to caress her with his modified arm, the hectocotylus. A male mates with a female by grabbing her, which sometimes completely obscures the female's vision, then transferring sperm packets by inserting his hectocotylus into her mantle cavity repeatedly. Mating continues until the female has had enough, and in at least one species, the female has to remove the over-enthusiastic male by force. Males will attempt copulation with members of their own species regardless of sex or size, but interactions between males are most often shorter in duration and end with the mounting octopus withdrawing the hectocotylus without packet insertion or struggle.