The blue-ringed octopuses (genus Hapalochlaena) are three (or perhaps four) octopus species that live in tide pools and coral reefs in the Pacific and Indian Oceans, from Japan to Australia (mainly around southern New South Wales and South Australia^[1]). They are recognized as one of the world's most venomous marine animals.^[2] Despite their small size and relatively docile nature, they can prove a danger to humans. They can be recognized by their characteristic blue and black rings and yellowish skin. When the octopus is agitated, the brown patches darken dramatically, and 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, and shrimp, and may bite attackers, including humans, if provoked.

Classification

The genus was described by British zoologist Guy Coburn Robson in 1929. There are three confirmed species of Hapalochlaena, and a fourth is still 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 - described in 1938 from a single specimen from the Bay of Bengal; the validity of this taxon has been questioned.^{[citation needed]}

Behaviour

An individual blue-ringed octopus tends to use its dermal chromatophore cells to camouflage itself until provoked, at which point it quickly changes colour, becoming bright yellow with blue rings or lines. The blue-ringed octopus spends much of its life hiding in crevices. Like all octopuses, it can change its shape easily, which helps it to squeeze into crevices much smaller than itself. This helps safeguard the octopus from predators and it may even pile up rocks outside the entrance to its lair. In common with other octopuses, the blue-ringed octopus swims by expelling water from its hyponome (funnel) in a form of jet propulsion. If the blue-ringed octopus loses an arm, it can regenerate it within six weeks.^{[citation needed]}

Feeding

Their diet typically consists of small crabs and shrimps, but they may also feed on fish if they can catch them. The blue-ringed octopus 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 exoskeleton, introducing its venom. The venom paralyzes the muscles required for breathing and movement. The octopus then rips away part of the shell with its beak and sucks out the flesh from the crustacean's exoskeleton.^{[citation needed]}

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 mantle, 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, however interactions between males are most often shorter in duration and end with the mounting octopus withdrawing the hectocotylus without packet insertion or struggle.^[3]

Blue-ringed octopus females lay only one clutch of about fifty eggs in their lifetime towards the end of autumn. Eggs are laid then incubated underneath the female's arms for approximately six months, and during this process she does not eat. After the eggs hatch, the female dies, and the new offspring will reach maturity and be able to mate by the next year.

Venom

Blue-ringed octopus from New South Wales, Australia

The blue-ringed octopus is 12 to 20 cm (5 to 8 inches), but its venom is powerful enough to kill humans. There is no blue-ringed octopus antivenom available.

The octopus produces venom that contains tetrodotoxin, 5-hydroxytryptamine, hyaluronidase, tyramine, histamine, tryptamine, octopamine, taurine, acetylcholine, and dopamine. The major neurotoxin component of blue-ringed octopus venom was originally known as maculotoxin but was later found to be identical to tetrodotoxin,^[4] a neurotoxin which is also found in pufferfish that is 10,000 times more toxic than cyanide.^[5] Tetrodotoxin blocks sodium channels, causing motor paralysis and respiratory arrest within minutes of exposure, leading to cardiac arrest due to a lack of oxygen. The toxin is produced by bacteria in the salivary glands of the octopus.^[6]

Treatment

First aid treatment is pressure on the wound and artificial respiration once the paralysis has disabled the victim's respiratory muscles, which often occurs within minutes of being bitten. Tetrodotoxin causes severe and often total body paralysis; the victim remains conscious and alert in a manner similar to curare or pancuronium bromide. This effect, however, is temporary and will fade over a period of hours as the tetrodotoxin is metabolized and excreted by the body. It is thus essential that rescue breathing be continued without pause until the paralysis subsides and the victim regains the ability to breathe on their own. This is a daunting physical prospect for a single individual, but use of a bag valve mask respirator reduces fatigue to sustainable levels until help can arrive.

Definitive hospital treatment involves placing the patient on a medical ventilator until the toxin is neutralized by the body. The symptoms vary in severity, with children being the most at risk because of their small body size. Because the venom primarily kills through paralysis, victims are frequently saved if artificial respiration is started and maintained before marked cyanosis and hypotension develop. Victims who live through the first 24 hours generally go on to make a complete recovery.^[7]

It is essential that efforts continue even if the victim appears not to be responding. Tetrodotoxin poisoning can result in the victim being fully aware of their surroundings but unable to breathe. Because of the paralysis that occurs they have no way of signaling for help or any way of indicating distress. Respiratory support, together with reassurance, until medical assistance arrives ensures that the victim will generally recover well.

The blue-ringed octopus, despite its small size, carries enough venom to kill 26 adult humans within minutes. Furthermore, their bites are tiny and often painless, with many victims not realizing they have been envenomated until respiratory depression and paralysis start to set in.^[8]

In popular culture

In Michael Crichton's novel State of Fear, an eco-terrorist group uses blue-ringed octopuses as a difficult-to-detect assassination technique, by placing an octopus kept in a plastic bag full of water on their victims and allowing the octopus to bite, killing the victim a few minutes later. Several victims of the group are dispatched in this way.

References

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