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Papuan cuttlefish (Sepia papuensis) raising four of its arms (upper centre) as a warning signal. It has also changed its skin colouration to a vivid red. This cuttlefish uses well developed eyes to detect danger, it can then instantly modify its skin colouring and pattern. This camouflaging is possible as the skin contains special colour cells or chromatophores, changing their size darkens or lightens the skin, producing an almost infinite range of colours and patterns. Photographed off Mabul, Malaysia. (KEYSTONE/SCIENCE PHOTO LIBRARY/MATTHEW OLDFIELD)