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Blue-ringed octopus
The blue-ringed octopodes are three octopus species that live in tide pools
and coral reefs in the Pacific and Indian Oceans, from Japan to Australia.
Their primary habitat is around southern New South Wales, South Australia,
northern & south-western Western Australia.
They are recognized as one of the world's most venomous marine animals. Despite their small size,,
and relatively docile nature, they are dangerous to humans if provoked and handled,
because their venom contains tetrodotoxin, a neurotoxin powerful enough to kill humans.
They can be identified by their characteristic blue and black rings, and yellowish skin.
When the octopus is agitated, the brown patches darken dramatically, 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, shrimp, and other small crustaceans.
Classification
The genus was described by British zoologist Guy Coburn Robson in 1929.
There are four confirmed species of Hapalochlaena, and six possible species still being researched:
Behavior
Blue-ringed octopodes spend much of their time hiding in crevices whilst displaying effective
camouflage patterns with their dermal chromatophore cells. Like all octopodes,
they can change shape easily, which helps them to squeeze into crevices much smaller
than themselves. This helps safeguard the octopus from predators
and they may even pile up rocks outside the entrance to their lair.  [^]  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,
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 there 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 using muscles which are under 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. In common with other Octopoda,
the blue-ringed octopus swims by expelling water from a funnel in a form of jet propulsion.
Feeding
The blue-ringed octopus diet typically consists of small crabs, and shrimp,
but they may also feed on fish if they can catch them.
The blue-ringed octopus pounces on its prey, seizing it with its tentacles
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 paralyses the muscles required
for movement, which effectively kills the prey.
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.
Blue-ringed octopus females lay only one clutch of about 50 eggs in their lifetimes towards the
end of autumn. Eggs are laid then incubated underneath the female's arms for about 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.
 Toxicity 
The blue-ringed octopus, despite its small size, carries enough venom
to kill twenty-six adult humans within minutes. 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. No blue-ringed octopus antivenom is available yet,
making it one of the deadliest reef inhabitants in the ocean.
 Venom 
 [^]  The octopus produces venom containing tetrodotoxin, histamine, tryptamine, octopamine, taurine,
acetylcholine, and dopamine. The venom can result in nausea, respiratory arrest, heart failure,
severe and sometimes total paralysis, blindness, and can lead
to death within minutes if not treated. Death, if it occurs, is usually from suffocation due
to paralysis of the diaphragm.
The major neurotoxin component of the blue-ringed octopus is a compound that was originally known
as maculotoxin, but was later found to be identical to tetrodotoxin,
a neurotoxin also found in pufferfish, and in some poison dart frogs.
Tetrodotoxin is 1,200 times more toxic than cyanide. Tetrodotoxin blocks sodium channels,
causing motor paralysis, and respiratory arrest within minutes of exposure.
The tetrodotoxin is produced by bacteria in the salivary glands of the octopus.
A person must be in contact with the octopus to be envenomated. Faced with danger,
the octopus's first instinct is flee. If the threat persists,
the octopus will go into a defensive stance, and show its blue rings.
Only if an octopus is cornered, and touched, will a person be in danger of being bitten
and envenomated.
 Effects 
Tetrodotoxin causes severe and often total body paralysis.
Tetrodotoxin envenomation can result in victims 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. 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.
The symptoms vary in severity, with children being the most at risk,
because of their small body size.
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