How do octopus chromatophore cells change color?

Cephalopods, including octopuses, squid and cuttlefish, are part of an exclusive group of creatures in the animal kingdom who can change color based on their activity or surroundings. Other notable color-changers include seahorses, some amphibians and lizards (including the chameleon, naturally!)

Cephalopods have specialized cells in their skin called chromatophores. Each chromatophore cell has a stretchy sac called the cytoelastic sacculus that is filled with pigment, which can be red, yellow, brown or black in color. When the muscles around the cell tighten, they pull the pigment sac wider, meaning more pigment is visible on the octopus’ skin. Conversely, when the muscles relax, the pigment sac shrinks back to size, and less pigment is visible.