Brittle stars are covered in protective outer plates, but they also have another structure of internal plates. A particular species of brittle star seems to be able to use these internal plates for vision: it reacts to visual stimuli, like the presence of a predator or a safe place to hide.
Scientists hope we can improve existing technology and invent new technology by understanding how the brittle star uses these calcite lenses.
Burgess, Daniel S. (2014). Brittle Star Features Calcite Lenses. Photonics Media. Photonics Media, 10 Jan.
Ye, Xiaozhou, Fei Zhang, Yurong Ma, and Limin Qi. (2014). Brittlestar-Inspired Microlens Arrays Made of Calcite Single Crystals. Small. 1677-682.
Roach, John. (2001). Brittle Star Found Covered With Optically Advanced “Eyes”. National Geographic. National Geographic Society, 22 Aug. 2001.