How do octopi change colour

A.� Many octopuses, along with other cephalopods like squid and cuttlefish, can change colour. They do so by virtue of special pigment cells called chromatophores that can change size, varying the animal's skin colour and pattern. Chromatophores are connected to the nervous system, and their size is controlled by muscular contractions.

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Q.� Why change colour

A.� It's a perfect way to camouflage yourself or to startle and warn possible predators.

Some cephalopods also have the ability to create light as a means of confusing either prey or predators.

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Q.� They can produce light

A.� Yes, many marine animals use biologically produced light, officially known as bioluminescence.

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Q.� How do cephalopods produce light

A.� Basically by mixing chemical substances together, producing a reaction that creates a light-producing chemical.

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The chemicals involved are oxygen and luciferin. When an enzyme called luciferase is present, the oxygen and luciferin react and a new molecule forms, which glows in the ocean.

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Q.� What for

A.� Bioluminescence comes in handy for a number of things. It can effectively confuse or surprise a predator, allowing the animal to make a quick escape. It can also be used to either stun or lure prey. And last, but not least, light makes a very effective means of communication in the darkness of the deep.

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Q.� So octopi can see

A.� Yes, they have excellent eyesight. It's because their eyesight is so good that they're able to closely match themselves with the underlying seabed when creating colour patterns as a means of camouflage.

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Q.� How big is the biggest octopus

A.� Among the 200 species of octopus living in the world's oceans, the largest is the Pacific giant octopus that can weigh over 70 kilograms and has an arm span of more than nine metres.

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Q.� How can changing colour help this giant surprise prey or evade predators

A.� It's easy for an octopus to escape through a very small gap, as it has no bones or shell. Such effective camouflage ensures that an octopus can ambush small fish and crabs.

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Q.� 'Oct' obviously refers to the number eight, but what does the whole word mean

A.� The word 'octopus' means 'eight arms'.

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by Lisa Cardy