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Octopus tentacles react independently to light

We know that octopuses are highly intelligent creatures and to that knowledge we can add a new discovery, namely that the eight tentacles of an octopus respond independently of the octopus’s brain and eyes to recoil from light as it signifies potential danger.

In a study they illuminated a tentacle of an octopus without the octopus being aware of the light and they discovered that the tentacle retracted and moved away from the light in a defensive behaviour. This is a previously unknown behaviour and it was discovered by accident.


Octopus. Photo: Pixabay.

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A team of researchers in Israel were exploring the ability of octopuses to camouflage themselves. We know that their skin is covered in many specialised cells called chromatophores. These cells contain pockets of pigments of different colours. When these pockets are expanded or contracted they change colour and can match the colours and patterns of the habitat around the octopus to camouflage them.

Chromatophores are known to expand when placed in the light. They wanted to find out how this works so they shone a torch onto a common octopus which they had recently taken from the Mediterranean sea.

The octopus refused to cooperate. They found that every time they shone the light onto a tentacle the arm would move away. This happened when the octopus’s eyes couldn’t see the light. They were surprised.

They believe that this behaviour has evolved to stop their rangy limbs straying out of safe shadowy areas in their rocky habitat which would alert predators. It is a survival instinct behaviour.

Octopuses are very dextrous. They been seen to twist open the lid of a jam jar when inside the jam jar! And they can be a little bit naughty as well because they’ve been recorded in aquariums turning off the lights by squirting jets of water at the light bulbs.

In this test they wanted to make sure that the tentacles were detecting the light source themselves independently of the eyes and brain of the octopus. The tank in which the animal was kept was in the dark. They allowed the octopus to place a single tentacle through a narrow opening. The temptation was a piece of fish. When this tentacle detected a light source it recoiled. They did the test 10 times and the tentacle recoiled in 80% of those times.

The nervous system of an octopus is very different to that of a human’s. Each tentacle is able to operate independently. And when a tentacle finds food the other tentacles join in and they work together. It appears that decision-making is sometimes delegated to the animal’s limbs in which are two thirds of the octopus’s neurons.

Study published in the Journal of Experimental Biology. Study author: Dr Nir Nesher.