Squid Chromatophores

(YouTube link)

What you see here is a microscopic view of a squid’s surface, showing the action of its chromatophores.

Chromatophores are pigment-rich, light-reflecting cells found in amphibians, fish, reptiles and cephalopods, such as squid. The cells dictate eye and skin color and, in some species, allow the bearer to adopt a color-changing camouflage when stimulated by heat, stress and other factors — a process known as metachrosis. The camouflage is also used in communication.
Squid rapidly change color when the muscles surrounding a chromatophore-filled sac contracts and expands — when it contracts, the pigment appears denser, when it expands the color becomes muted and disappears. The squid changes its color according to exterior factors — such as a threat or the presence of a potential mate – because each chromatophore is linked to a nerve ending.

Marine biologist Michael Bok took advantage of a squid with skin cells still active despite being shipped on ice, to make this video. More