To flash mating displays, signal warnings, and disguise themselves from predators, cephalopods alter their appearance to take on wild patterns, colors, and shapes. Tens of thousands of organs called chromatophores form color patterns on the skin, similar to the way pixels form images on a computer screen. The chromatophores are controlled by nerves, allowing color change to occur instantaneously.
Chromatophores are sacs of pigment surrounded by muscles. When the muscles around the chromatophores are relaxed, the pigment is concentrated into a tiny point, making the area of skin appear white. When the muscles contract, the pigment stretches out and colors the skin. (Imagine a small, colored dot on a rubber band. When the rubber band stretches, the area of color expands.)
Chromatophores contain red, orange, yellow, black, and brown pigments. But a set of mirror-like cells called iridophores allows cephalopod skin to assume all the rich and varied colors of its environment. Because cephalopods are thought to be colorblind, it is probably not the pigmented chromatophores that enable them to match their backgrounds, but rather the iridophores reflecting the brightness of the environment.
Texture, posture, and movement are other important elements of disguise. Projections in the skin called papillae allow cephalopods to resemble various textures. For example, some benthic octopuses will acquire a smooth, mottled appearance to blend in with sandy oceans bottoms or a bumpy texture to match the surface of a coral reef. Squid dangle their arms downward to disguise themselves as drifting pieces of seaweed. Other cephalopods even use pebbles or shells as props for especially elaborate acts of subterfuge.
Not all cephalopods blend into their surroundingsâ€”some species let their colors shine. When disturbed, the flamboyant cuttlefish (Metasepia pfefferi) parades vibrant patches of yellow, white, and red. Its bright exterior probably advertises an unpleasant-tasting or poisonous nature, a device also used by poison dart frogs and monarch butterflies.