Mantis shrimp have the best eyes of the animal kingdom: they can see a wider range of colours than any other creature, from ultraviolet nearly all the way through to infra-red.
Human beings have three types of cone cell used to detect colour: each one detects a different range that corresponds roughly to red, green, and blue wavelengths. The brain combines information from all three to work out the hue of whatever it is we’re looking at.
(Side note: colour blind people typically have trouble with one or more of their cone cells. People with protanopia, for example, have no red cones and so cannot easily distinguish between green, yellow, and red; people with deuteranomaly have green cones that detect a different range than the green cones of non-colour blind people.)
Because most of us have only three types of cone cell, we cannot detect colours outside of those ranges. In comparison, the mantis shrimp is a colour-detecting maestro.
Mantis shrimp eyes have a ridiculously high range of cones – up to sixteen different cones in some species, detecting sixteen different colour ranges. They can see down to ultraviolet, of course, and up into the range of “far-red” (basically, the red immediately before infra-red). But the power of mantis shrimp eyes don’t stop there.
Mantis shrimp can see polarised light (a trait they share with bees, who use that trick for navigational purposes – but I’m going to write about that another time) and each eye has trinocular vision. That means a one-eyed shrimp still has depth perception.
What do they need all this sophisticated hardware for? Hunting and mating rituals, apparently. Which is pretty much the explanation for most animal characteristics.