The octopus can see with its skin

Octopuses are well known for changing the colour, patterning, and texture of their skin to blend into their surroundings and send signals to each other, an ability that makes them both the envy of, and inspiration for, army engineers trying to develop cloaking devices. As if that wasn’t already impressive enough, research published today in the Journal of Experimental Biology shows that octopus skin contains the pigment proteins found in eyes, making it responsive to light.

These clever cephalopods can change colour thanks to specialised cells called chromatophores, which are packed in their thousands just beneath the skin surface. Each of these cells contains an elastic sac of pigmented granules surrounded by a ring of muscle, which relax or contract when commanded by nerves extending directly from the brain, making the colour inside more or less visible.

Octopuses are thought to rely mainly on vision to bring about these colour changes. Despite apparently being colour blind, they use their eyes to detect the colour of their surroundings, then relax or contract their chromatophores appropriately, which assume one of three basic pattern templates to camouflage them, all within a fraction of a second. Experiments performed in the 1960s showed that chromatophores respond to light, suggesting that they can be controlled without input from the brain, but nobody had followed this up until now.

Evolutionary biologists Desmond Ramirez and Todd Oakley of the University of California, Santa Barbara therefore removed patches of skin from 11 hatchling and adult bimac octopuses (Octopus bimaculoides), mounted them onto Petri dishes with insect pins, and used light emitting diodes to shine light of different wavelengths onto the skin preparations. They noticed that the chromatophores expanded quickly, and remained expanded, pulsating rhythmically, when exposed to continuous bright white light. By contrast, red light caused slow, rhythmic muscle contractions, but not chromatophore expansion.

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http://www.theguardian.com/science/neurophilosophy/2015/may/20/octopus-skin-contains-light-sensors?CMP=share_btn_tw