Don't mess with the blue-ringed octopus. The golf ball-sized cephalopod, which lives in the Pacific Ocean along shallow shores, carries a neurotoxin that can kill an adult human within minutes. But before it bites, releasing its venomous saliva through its beak, the octopus sends out a warning—a flash of bright blue rings—that seems to suddenly iridesce all over its body. A study published today inThe Journal of Experimental Biology reveals how the creature puts on its colorful show: by flexing its muscles. It turns out that the blue-green rings are always there, but pouches of skin conceal their iridescence when the octopus is relaxed. When the octopus gets agitated, it releases one set of muscles and tenses another to get the pouches out of the way and reveal its iridescence. The blue-ringed octopus's brawny approach is unique—all other cephalopods use sacs of pigment, called chromatophores, to change their colors.
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