Chitons See With Eyes of Rock
Posted on April 15, 2011
The lined chiton lives about 50 feet below the water's surface near Whidbey Island, Washington. The three-inch-long mollusks use eyes of rock to see predators, but they cannot see very well. Human vision is about a thousand times sharper than chiton vision. Chitons have hundreds of eye-like structures with lenses made of aragonite, a tpe of rock. Chitons also make their shells from aragonite.
Sonke Johnsen, associate professor of biology at Duke, says, "It's surprising how these creatures make their eyes from rocks. But it seems like an easy way to evolve eyes, by using what you've already got."
Johnsen and Daniel Speiser, a postdoctoral fellow in the Department of Ecology Evolution and Marine Biology at UC Santa Barbara, tested the creatures vision by showing them gray slides and black disks.The chitons did not respond when shown gray screens. However, they clamped down when they were shown a black disk three centimeters or larger in diameter. The researchers say this means human vision is about a thousand times sharper than chiton vision.
LiveScience has some closeup images of chiton rock eyes here.