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.
For more info:
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.