The filters are made of something called MAAs, or mycosporine-like amino acids. These amino acids are common in the skin of marine organisms, and are usually used to absorb cell-damaging UV light.
Mantis shrimp, however, have repurposed the MAAs to absorb certain UV wavelengths in the eye. Each different filter removes different portions of the light, meaning that certain wavelengths only hit certain areas of the eye.
"It pretty nicely narrows their sensitivity by removing certain components of the spectrum," Bok said. The filtering thus enables the mantis shrimp to detect multiple wavelengths with only two visual pigments.
"It's a very, very strange system, and it's very alien compared to ours," Bok said.
Bok, who is currently doing fieldwork on the Great Barrier Reef in Australia, said the next goal is to study how mantis shrimp use their unusual visual system. They might use visual information to communicate, to hunt or to avoid predators, he said.
"It's an interesting question," he said. "Why do they need this? What could it possibly be used for?"