What amazing biological adaptations might we discover when we finally find extraterrestrial life? Even within Earth’s biosphere, we’ve identified one incredible species after the other. One especially intriguing example is a chiton—a type of mollusk—that uses minerals as eyes.
The chiton Acanthopleura granulate looks like a fossil that became rock, but is actually a living organism that thrives in the Caribbean and uses heavy armor to protect itself from predatory fish. Previous work already hinted that smoothly aligned aragonite, a type of calcium carbonate mineral, could function in the chiton as an eye. Each eye lens is less than a tenth of a millimeter in size, and the animal has hundreds of them. What was unclear was whether this set-up, using aragonite instead of proteins for “eyes,” could create an actual image.
Now Ling Li and coauthors have found that it can. They determined that images could be formed of objects such as a predatory fish by individual mineral lenses in water. The rock lenses form clear images of a 20-centimeter (5-inch) long fish from a distance of 30 cm (7.5 inches). The images have enough resolution to allow the chiton to react to the fish by clamping down to the rock substrate so that it is not easily dislodged.
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