Cephalopods are soft bodied and have no external shells to protect them, so they are easy prey for hungry hunters like fish, sharks, and seals. Defense strategies used by cephalopods include techniques in camouflage that enable them to alter both the color and texture of their skin. As a cephalopod moves across the seafloor looking for food, the color of its skin changes almost instantly. This remarkable ability is mediated by the animal’s advanced nervous system.
If startled, a cephalopod’s eyes relay messages to the body telling it to go into a defensive mode. The eyes take in the color of the surroundings, then send nerve impulses to special skin cells called chromatophores that contain bags of pigment. When the bags expand, the color becomes intense; when they contract, the color fades to tiny dots. Camouflage is achieved by expansion of some chromatophores and contraction of others.
If there was a contest to judge the most creative use of chromatophores, the mimic octopus would win. The repetoire of this master of camouflage includes sea snakes, lionfish, and other poisonous animals. To imitate a lionfish, the cephalopod turns blue and flares its legs to look like poisonous fins. To impersonate a sea snake, the octopus changes its colors to yellow and black bands, tucks its body and all but two legs into a hole, then waves the two exposed legs in snake-like fashion.