The common octopus can produce elaborate colour patterns and highly complex skin textures capable of matching a wide range of backgrounds from sand and reef rubble, through to spiked corals and seaweeds. Their skin changes almost instantaneously as they move over different substrates on the sea floor. Colour changes are carried out by small, elastic, pigment-filled sacs, known as chromatophores. A square centimetre of skin may contain hundreds of chromatophores, in up to five colours in certain species. Each chromatophore is surrounded by a ring of muscle fibres, all of which are under the rapid and coordinated control of the large optic lobes of the brain.