(Santa Barbara, Calif.) Using eyes made of a calcium carbonate crystal, a simple mollusk may have evolved enough vision to spot potential predators, scientists say.
Daniel Speiser, a postdoctoral fellow in the Department of Ecology Evolution and Marine Biology at UC Santa Barbara, studied mollusks that he collected in the Florida Keys. His research of their vision, performed during his graduate studies at Duke University, resulted in a study published today by Current Biology.
The three-inch-long mollusks, called chitons, have hundreds of eye-like structures with lenses made of aragonite, a type of rock. It's the first time scientists have found an animal that makes eye lenses from aragonite and not the rock's close cousin, calcite.
Scientists discovered the chiton's unique eyes decades ago. But it wasn't clear whether chitons used these eyes to see objects overhead, or simply to sense changes in light. "Turns out they can see objects, though probably not well," said Speiser.
"It's surprising how these creatures make their eyes from rocks," said Snke Johnsen, associate professor of biology at Duke. Most animals make their eyes from cells with proteins and chitin. "But it seems like an easy way to evolve eyes, by using what you've already got," he said. Chitons also make their shells from aragonite.
Johnsen and Speiser studied West Indian fuzzy chitons, or Acanthopleura granulata, which have flat shells made of eight separate plates. Hundreds of tiny lenses on the surface of the plates cover clusters of light-sensitive cells beneath.
To test the creature's vision, Speiser placed individual chitons on a slate slab. When left undisturbed, they lift part of their armored, oval-shaped body to breathe. At this point, Speiser showed them either a black disk ranging from .35 centimeters to 10 centimeters in diameter or a corresponding gray slide that blocked the same amount of light. The disk or slide
|Contact: Gail Gallessich|
University of California - Santa Barbara