Mantis shrimp, or stomatopods, are colorful marine crustaceans renowned for their impressive visual system, and of course that feisty punch to take down prey. Now, the story of these marine ninjas gets even more interesting with the discovery that they use a biological sunscreen to tune UV vision. The study has been published in Current Biology.

Mantis shrimp have remarkably complex visual systems. They have 16 or more different photoreceptors which endow them with not only color vision but the ability to detect UV and polarized light also. In fact, to our knowledge, they are the only animals that can detect circularly polarized light, which is where light waves form a rotating spiral. While scientists knew that these crustaceans had UV vision, little was known about the components of this system until now.

Researchers discovered that while mantis shrimp have only two UV visual pigments in their retinas, they have four UV-specific optical filters in their crystalline cones, which are conical bodies that function as a lens. These filters, combined with the two pigments, combine to spectrally tune six UV receptors. Furthermore, it was discovered that the filters were made up of mycosporine-like amino acids, or “nature’s sunscreens,” which are often found in the skin or exoskeleton of various marine organisms in order to protect them from UV damage. Mantis shrimp, however, use them in a unique way, preventing certain wavelengths of light from reaching the UV photoreceptors and thus 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,” said lead author Michael Bok in a news-release.

Why precisely mantis shrimp require this complex visual system remains somewhat of a mystery. It is possible that this UV vision could be used to spot otherwise hard-to-see prey as many organisms absorb UV light. Alternatively, this intricate color and polarization visual system could allow the organism to sense and respond to a variety of inputs without the need for a complex information processing system.

Trying to envisage how mantis shrimp see the marine world still remains pretty difficult, however, given the vast differences between their visual processing system and ours. 

Image credit: Nazir Amin, via Wikimedia Commons. 

Header image: "Mantis Shrimp" by Klaus Stiefel, via Flickr, user in accordance with CC BY-NC 2.0.