Mantis shrimps view the underwater world in a new light: Sea creatures use 'biological sunscreen' to see UV colours
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Mantis shrimps view their underwater world in a whole new light, seeing ultraviolet (UV) colours far beyond the range of human vision, scientists have learned.
And the secret to a mantis shrimp's incredible ultraviolet vision is, strangely enough, biological sunscreen.
The creatures' bulging eyes contain built-in filters made from a biological sunscreen used by other marine animals to shield themselves against UV rays.
Mantis shrimps view their underwater world in a whole new light, seeing ultraviolet (UV) colours far beyond the range of human vision, scientists have learned. And the secret to a mantis shrimp's incredible ultraviolet vision is, strangely enough, UV-blocking sunscreen
'The mantis shrimp visual system contains six types of photoreceptors functioning completely outside the visual range of humans,' said Michael Bok, from the University of Maryland.
'The UV filters block certain wavelengths of light from reaching the photoreceptors, chromatically shifting their sensitivity.
'The effect is akin to putting red-tinted glasses over your eyes that block other wavelengths of light, except this is being done at the photoreceptor cellular level in shrimp.'
The creatures' bulging eyes contain built-in filters made from a biological sunscreen used by other marine animals to shield themselves against UV rays
THE MANTIS SHRIMP: KEY FACTS
Mantis shrimp can reach 30 centimetres (12 inches) in length.
They are usually found in shallow tropical or subtropical waters, with some species of Mantis shrimp occasionally found in sub-Antarctic water
Called 'sea locusts' by ancient Assyrians and 'prawn killers' they can inflict painful gashes if handled carelessly.
Eyes of mantis shrimp are located on the long stalks that can move independently.
These typically solitary sea creatures spend most of their time hiding in rock formations.
Some species of mantis shrimp, known as 'smashers;, are equipped with club-like claws that can strike with the speed of a bullet.
A few groups of mantis shrimp are monogamous and spend up to 20 years together.
Why the mantis shrimp needs such a sophisticated visual system is a mystery.
The creatures use their eyes to navigate and spot predators on the reefs where they live.
They also have complex social interactions that are thought to involve fluorescent patterns on their bodies.
Their eyes contain 16 or more types of photoreceptors that help them make sense of complex visual signals without the need for a big brain.
'The way their eyes are built and how visual information is processed in their brains is so fundamentally different from humans that it is very difficult to conceptualise what the world actually looks like to them,' said Mr Bok, whose research is reported in the journal Current Biology.
In January, a study by the Queensland Brain Institute, crushed the illusion that complex eyes with more colour channels mean better colour vision. 
The team say the Mantis shrimp sees the world in an entirely different way to any other animal
Researcher Hanne Thoen found that the mantis shrimp (Haptosquilla trispinosa), which has 12 colour channels, has worse colour vision than humans, which have three colour channels.
'Theoretically, mantis shrimp should be far better at distinguishing colours than we are,' Ms Thoen said.
'Human brains – and all other animals including birds, monkeys, frogs and fish – determine the colours of objects by comparing the relative excitation of inputs.
'For instance, in humans this is red, green and blue
'The critical finding is that mantis shrimp do not do this, and this means their way of encoding colour is different to all other animals known.'
Researcher Hanne Thoen found that the mantis shrimp (Haptosquilla trispinosa), which has 12 colour channels, has worse colour vision than humans, which have three colour channel
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