Video: Sea creature makes a thousand eyes from its shell

Although chitons look very simple, these mollusks have a very sophisticated shell. Its outer layer contains up to 1000 tiny eyes, each a bit smaller than the period at the end of this sentence. In Science today, researchers describe how chitons build the lenses of their eyesfrom the same hard mineral that armors their shells. As the video above illustrates, these eyes actually form images, demonstrating how this remarkable material can perform two jobs—seeing and protecting—at once. That’s something that materials scientists would like to be able to do better, so this study helps show them the way. The scientists explored how the eyes are made and how well they work using high-resolution microscopy and x-ray techniques, as well as computer modeling. They found that although most of the shell consists of small, irregularly arranged crystals, the oblong lens is made of large crystals, aligned to allow light through relatively unimpeded. Up to 100 photo-sensitive cells form a retina, which is positioned so any bird, fish, or other predator up to 2 meters away registers as an image there. When a chiton sees these predators, it clamps down tightly to the rock. Chitons can't move very fast, so they depend on their hard armor to keep them safe. The eyes are chinks in the armor, but as an improved advanced warning system, they more than make up for causing these weak spots. 

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