How does a blue-ringed octopus flash its rings?

Cephalopods have colour-changing chromatophores on their skin, which allows them to camouflage themselves — but the blue-ringed octopus has a different trick up its tentacle.

(Blue-Ringed Octopus, Mabul Island, Malaysia image by Angell Williams, CC BY 2.0)

Cephalopods have colour-changing chromatophores on their skin, which allows them to camouflage themselves — but the blue-ringed octopus has a different trick up its tentacle.

The blue-ringed octopus is tiny and gorgeous — but, as we Australians know, those dainty blue iridescent rings are a warning sign. The octopus' venom is the deadliest in the world, enough to kill an adult human within minutes via a paralysis that shuts the body down completely, and there is with no anti-venom — victims have to be intubated and kept alive via artificial respiration until the venom passes from the body.

But how this octopus shows the rings is different to how squids and other octopodes camouflage themselves, discovered Lydia Mäthger, a biologist at the Marine Biological Laboratory in Woods Hole Oceanographic Institution, Massachusetts. She and a team of researchers filmed the octopus at super-slow speeds to find out the secret.

The colour in the rings is not caused by chromatophores, but iridophores — an iridescent layer, usually under the skin of the cephalopod, that shifts to reflect light. In the blue-ringed octopus, the "rings" are sections of the skin where the iridophores aren't covered by the chromatophore layer. The circle of skin inside the ring has a direct neural connection, and the octopus can contract it at will, revealing the glowing blue ring underneath.

Check it out in the video below. Aren't cephalopods amazing?

Via blogs.scientificamerican.com

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