Shrimp can see beyond the rainbow

Wed May 14, 6:31 AM ET

LONDON (Reuters) - A giant shrimp living on Australia's Great Barrier Reef can see a world beyond the rainbow that is invisible to other animals, scientists said on Wednesday.

Mantis shrimps, dubbed "thumb splitters" by divers because of their vicious claws, have the most complex eyes in the animal kingdom, capable of seeing colours from the ultraviolet to the infrared, as well as detecting other subtle variations in light.

They view the world in up to 12 primary colours -- four times as many as humans -- and can measure six different kinds of light polarisation, Swiss and Australian researchers reported.

Polarisation is the direction of oscillation in light waves.

Just why Gonodactylus smithii needs this level of rarefied vision is unclear, although the researchers suspect it is to do with food and sex.

"Some of the animals they like to eat are transparent and quite hard to see in sea-water, except they're packed full of polarising sugars. I suspect they light up like Christmas trees as far as these shrimp are concerned," said Andrew White of the University of Queensland.

And the shrimps probably use tiny changes in colour and polarisation to send sexual signals between males and females, the researchers believe.

Their findings were published online in the Public Library of Science journal PLoS ONE, at http://www.plosone.org/doi/pone.0002190