A cave dwelling crustacean that is extremely sensitive certain waves of light because it almost solely uses its eyes to find the small bits of mold that it uses to eat. The mold reflects a certain wavelength color that the crustacean can see. Bad thing is it needs light to see the mold, but the requirement for seeing the mold is having sensitive eyes.
To protect its eyes from the main force of light it has created a super reflective shell that reflects all the light away from its eyes keeping it from being in direct light. At the same time as saving its sensitive eyes, the shell also splits the light waves into a rainbow and spreads it out in front of it so that the specific wavelength light that reflects off the mold is concentrated.
The snail-like creatures can grow up to a foot long by 3/4 foot high but are very rare.
The shell is a favorite among royalty for its rainbow creating ability.