Shrimps view world in new light
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.
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 visual system contains six types of photoreceptors functioning completely outside the visual range of humans," said Michael Bok, from the University of Maryland in the US.
"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."
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.
Some species of mantis shrimp, known as "smashers", are equipped with club-like claws that can strike with the speed of a bullet.