Primitive Sea Creature Sports Eyes Made of Rock

A tiny sea mollusk uses eyes made of a calcium carbonate crystal to spot predators lurking above, researchers say of the first such rocky lenses found in the animal kingdom.

While scientists had discovered the hundreds of eye-like structures on the surface of this armored mollusk, called a chiton, decades ago, they didn't know what they were made of or whether they could actually see objects or just sensed light. [Image of chiton eyes]

"Turns out they can see objects, though probably not well," said study researcher Daniel Speiser, who recently became a postdoctoral fellow at the University of California, Santa Barbara.

For comparison, the study found that chiton vision would be the equivalent of humans looking in the sky and seeing a disk the diameter of 20 moons, making human vision about a thousand times sharper than chiton vision, the researchers said. [Jellyfish Have Human-Like Eyes]

Chitons first appeared on Earth more than 500 million years ago. But according to the fossil record, the oldest chitons with eyes didn't emerge until the last 25 million years, making their eyes among the most recent to evolve in animals.

The eyes likely evolved so chitons could see and defend against predators, Speiser said ...

via Primitive Sea Creature Sports Eyes Made of Rock | Chitons & Primitive Creatures | Evolution of Vision | LiveScience.