Fantastic read from The Atlantic:

Mantis shrimp have unusual eyes. Mostly famously, they have 16 color receptors, compared to a human’s three. Oddly, they are not that good at distinguishing between colors, but they can detect another property of light invisible to humans: polarization.

While polarization can be difficult to intuit, you can imagine light waves as a bunch of different strings that each have one end attached to a wall. If you shake them randomly, they will vibrate in every direction; that is how non-polarized light behaves. If you only the shake the strings up and down, restricting vibrations to one direction, then that is like vertically polarized light. Light can be polarized in different directions. Polarized sunglasses take advantage of this phenomenon: They reduce glare by filtering out horizontally polarized light that bounces off a road or water surface.

In the ocean, light can be also be polarized when it bounces off molecules in water. Mantis shrimp can see up to six types of polarization: horizontal, vertical, two diagonals, and two types of circular polarization, in which a light wave spirals clockwise or counterclockwise. (They are the only animals known to see circularly polarized light.) Gruev likens it to wearing “six different miniature polarized sunglasses.” So Gruev and his team essentially miniaturized polarized lenses and put them inside a video camera.

Read more from The Atlantic, check out Bioinspired polarization vision enables underwater geolocalization and see more from NewsAtIllinois on YouTube. We also highly recommend this pretty recent Radiolab episode about Mantis Shrimp.