A serious threat in the coastal waters of Australia for those who wish to explore is the little blue ring octopus. They are currently recognized as one of the world's most venomous marine animals. This small creature, about the size of a golf ball, or even smaller at times, is highly toxic to humans and there is no known antivenin for the venom of the Blue Ring Octopus, which is highly poisonous. The venom of the Blue Ring Octopus contains neuro toxins, and can lead to paralysis, and will, if left untreated, end up in cardiac arrest for the victim.
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. 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.
Their diet typically consists of small crab and shrimp, but they may also feed on fish if they can catch them. They pounce on their prey, paralyze them with venom and use their beaks to tear off pieces. 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, a neurotoxin which is also found in pufferfish and cone snails that is 10,000 times more toxic than cyanide. 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. There is no blue-ringed octopus antivenom available.