When the muscles around the cell tighten, they stretch the pigment sac wider, which means more pigment is seen in the octopus's skin. Conversely, when the muscles relax, the pigment sac returns to its size and less pigment is seen. Octopuses can change color because they have chromatophores, tiny organs that change color and are scattered all over the octopus's skin. The most obvious reason that such a soft-bodied animal would change color is to hide from predators, and octopuses are very good at this.
They can change not only their color, but also the texture of their skin to match rocks, corals, and other nearby objects. They do this by controlling the size of the projections on the skin (called papillae), creating textures ranging from small bumps to high peaks. The result is a costume that makes them almost invisible; can you see the octopus in the video above? However, color change is just one tool in an octopus's arsenal of defenses; it can also spray ink and quickly escape through any hole its hidden beak bone may pass through. Just under the skin, octopuses have thousands of cells called chromatophores.
Each of these cells has a small sac filled with a red, orange, brown, yellow or black pigment and, by stretching or squeezing these sacs, they can quickly change the brightness of each of these colors. Believe it or not, the secret to an octopus changing color is hidden inside its skin. More specifically, octopuses have special cells called chromatophores in their skin. Chromatophores are small cells that contain pigments that are controlled by a series of muscles and nerves.
These small elastic colored sacks can be stretched or squeezed. Octopuses have specialized cells below the surface of the skin known as chromatophores. Each chromatophore has an elastic sac called a cytoelastic saccule in its center. Each of these bags is filled with pigments of different colors: red, yellow, black or brown.
In addition to all those reflectors and pigments, octopus skin also has the ability to quickly change its texture using small muscle bundles called papillae. Some 2,400 years ago, Aristotle, the ancient Greek philosopher who is often considered one of the founding fathers of modern science, wrote down detailed observations of octopus camouflage, the first person known to do so, Leila Deravi, a biochemist at Northeastern University in Massachusetts who studies octopus camouflage mechanics, he told Live Science. Octopuses can mimic other neighboring animals and habitats and, in doing so, can be very effectively camouflaged. These iridophoric cells are filled with hundreds of tiny mirror-like structures called reflectosomes, which reflect light back through the octopus's skin, allowing colors to appear brighter if desired.
However, for species that depend on color change, adapting their hue is an inherent skill that is available to them from the moment they are born (as you can see in the video clip below of a hatching octopus at the Virginia Aquarium & Marine Science Center). When the muscles are relaxed, the pigment sac returns to its normal size and the pigments are less noticeable, so the octopus returns to its original color unchanged. When the octopus decides to turn brown, the brown sacs extend to the surface in milliseconds, making the color dominant. In addition to their donut-shaped brain, octopuses have brain bags, or nodules, all over their bodies and all over their arms, Deravi said.
The Caribbean reef octopus (Octopus briareus) has a fantastic color screen using its iridophores by reflecting a blue-green color similar to metallic around its eye and on its webs. One of the best examples is the extremely venomous blue-ringed octopus (Hapalochlaena lunulata), which lives in tidal pools in the Pacific and Indian oceans from Japan to Australia. In addition to going unnoticed by their prey, octopuses can also use surprising displays, where they break camouflage and stun their prey with drastic and rapid color transitions before quickly catching them, Mather said. Certain colors and patterns within the animal kingdom indicate something dangerous or even poisonous, so some octopuses warn other animals not to even think about eating them.
The intensity of this reflective layer is controlled by the upper chromatophores, providing the octopus with additional color options, including disruptive camouflage if desired. For example, slippery glass octopuses have lost all their chromatophores and have become almost completely transparent. . .
