Cuttlefish are marine animals of the order Sepiida. They belong to the class Cephalopoda, which also includes squid, octopuses, and nautiluses. Cuttlefish have a unique internal shell, the cuttlebone. Despite their name, cuttlefish are not fish but molluscs.

Cuttlefish are sometimes referred to as the “chameleons of the sea” because of their remarkable ability to rapidly alter their skin color – this can occur within one second. Cuttlefish change color and pattern (including the polarization of the reflected light waves), and the shape of the skin to communicate to other cuttlefish, to camouflage themselves, and as a deimatic display to warn off potential predators. Under some circumstances, cuttlefish can be trained to change color in response to stimuli, thereby indicating their color changing is not completely innate.

As well as being able to influence the color of light as it reflects off their skin, cuttlefish can also affect the light’s polarization, which can be used to signal to other marine animals, many of which can also sense polarization. It has been suggested that although cuttlefish (and most other cephalopods) lack color vision, high-resolution polarisation vision may provide an alternative mode of receiving contrast information that is just as defined.