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Skin camouflage is controlled by chromatophores in the skin. The muscular contraction and expansion of the chromatophores changes the apparent concentration of the pigment, so when the muscles contract, the chromatophore and pigment is concentrated in a smaller area, thus becoming more apparent. All species have chromatophores with a variety of pigments including, yellow, orange, red, blue and black. This effect is then enhanced by layers of reflector cells called iridocytes which differentially reflect light.

The chromatophores are controlled by the nervous system and are triggered by hormones, while the initial stimulus seems to by visual. Colour change varies greatly among species, some such as the cuttlefish changing colour as the background changes. Most changes, however, appear to be behavioural, i.e. courtship or when alarmed. Many of the deep and mid-water squid are also bioluminescent, with photophores arranged in patterns over the body. This bioluminescence may be intrinsic, or it may be produced by symbiotic bacteria.

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Websites produced by students on the MSc Palaeobiology programme in the Department of Earth Sciences at the University of Bristol for academic year 2004-5