Today’s special animal friend is the blue-ringed octopus, the genus Hapalochlaena. There are four listed species of this extremely venomous octopus living in coral reefs and tidal pools in the Pacific and Indian Oceans. An additional six possible species are being studied. These may prove to be distinct species, or they may be individuals of the known species, some of which are only slightly “known”: one, Hapalochlaena nierstraszi, has been observed only twice in the Bay of Bengal, once in 1938 and once in 2013.
Blue-ringed octopi are from 5 to 8 inches long and weigh a couple of ounces. They hide in crevices in rock or coral, sometimes using their tentacles to pile rocks at the entrance for additional protection. Their skin in normally yellowish to grayish, with darker mottled patterns making very effective camouflage. They eat small crustaceans or fish, especially ill or injured fish, which they seize with their arms, bite with a strong beak, and inject with venom which paralyzes the prey.
Their eponymous blue rings become visible only when the octopus is agitated or threatened. In less than one second, their skin becomes brighter, often yellow, and the dark patches become darker, while the bright blue rings are revealed. These rings are normally concealed by skin due to contractions of the octopus’s muscles; that is, the appearance of the rings is not a skin color change but a shift in the musculature. The rings of the greater blue-ringed octopus, Hapalochlaena lunulata, have multi-layered light reflectors called iridophores, which reflect blue-green light over a wide viewing area.
The venom of the blue-ringed octopus is called tetrodotoxin or TTX. It is a neurotoxin (affecting the nervous system) that is also found in pufferfish, porcupinefish, and several other animals. The toxin is produced by bacteria such as Pseudoalteromonas, Pseudomonas, and Vibrio, which either infect that animal or coexist in symbiosis. This chemical is a “sodium channel blocker,” which causes paralysis of muscles by blocking electrical transmission through the nervous system. The mechanism was identified by researchers at Duke University in 1964.
Despite the extreme toxicity of the blue-ringed octopus’s bite, human deaths are very rare. People are very unlikely to encounter it in the wild; the most likely victims of bites are research biologists or specimen collectors. Although there is no antivenin, treatment such as CPR can keep a bite victim alive until the venom is metabolized and excreted, usually within 24 hours.
Thanks!
That was really cool! That was pretty interesting about the tetrodotoxin. There is at least one episode of Death in Paradise where that toxin is used as the murder weapon.