Variable coloration by chromatophores Animal coloration

fish , frog melanophores cells can change colour dispersing or aggregating pigment-containing bodies.

chromatophores special pigment-containing cells may change size, more retain theiroriginal size allow pigment within them become redistributed, varying colour , pattern of animal. chromatophores may respond hormonal and/or neurobal control mechanisms, direst responses stimulation visible light, uv-radiation, temperature, ph-changes, chemicals, etc. have been documented. voluntary control of chromatophores known metachrosis. example, cuttlefish , chameleons can rapidly change appearance, both camouflage , signalling, aristotle first noted on 2000 years ago:

the octopus ... seeks prey changing colour render colour of stones adjacent it; when alarmed.

squid chromatophores appear black, brown, reddish , pink areas in micrograph.

when cephalopod molluscs squid , cuttlefish find against light background, contract many of chromatophores, concentrating pigment smaller area, resulting in pattern of tiny, dense, spaced dots, appearing light. when enter darker environment, allow chromatophores expand, creating pattern of larger dark spots, , making bodies appear dark. amphibians such frogs have 3 kinds of star-shaped chromatophore cells in separate layers of skin. top layer contains xanthophores orange, red, or yellow pigments; middle layer contains iridophores silvery light-reflecting pigment; while bottom layer contains melanophores dark melanin.