Gordon Hendler is into echinoderms -- starfish and their cousins -- and he's always thought they seemed a little alien. Not because they look like stars. And not just because their skeletons are on the outside.

Thirty years ago while diving in the Caribbean, Hendler noticed that brittlestars, one type of echinoderm, can change color in dramatic fashion when exposed to light or shadow. So for 30 years he's been trying to figure out why.

Now serving as Curator of Echinoderms at the Natural History Museum of Los Angeles County, Hendler and some colleagues are on to a likely answer:

The small sea creatures don't just wear their bones on their sleeves: They are also nearly covered in eyes.

The researchers found that a substance called calcium carbonite -- the stuff that makes the armor-like plating of a brittlestar's exoskeleton -- also figured out a way to make miniature crystals that serve as light sensors.

The tiny crystals attach themselves into arrays of seven and cover most of a brittlestar's body. Handy for spotting predators, the researchers point out. Pigmented cells cover the lenses and control how much light passes through them.

Closer examination reveals bundles of nerves that are presumed to be photoreceptors because they are curiously positioned just below the surface of the skeleton and exactly where the light is focused -- a mere 5 microns behind the lenses. A human hair is about 50 microns thick.

A brittlestar does not use each lens to see in the traditional sense. But combined, the lenses may form a kind of compound eye that can serve as a rudimentary warning system.

"This is the first example, so far as I am aware, of an organism with a body surface that is largely covered with crystalline lenses that are part of a complex photoreceptor system," Hendler said. "This is an extraordinary adaptation that had not been appreciated, and it certainly is an example of how varied life is as a result of evolution."

Hendler said the finding widens the range of evolutionary adaptations that scientists might eventually expect to find on other planets. And it is a reminder that there's plenty left to learn about biology on this planet, too.

"We haven't yet seen or named most of the organisms that live with us on Earth," Hendler said. "And we know precious little about the basic biology of the relatively few organisms that can be identified."

Technologists who've never seen brittlestars have developed similar microlensing arrays in recent years. The devices are used for precision applications like routing optical signals or creating directional displays in the world of micro-optics. But each crystal in the brittlestar is a near-perfect lens far smaller than anything that can be created with current human technology, according to the new study.

A scientist who could reproduce the brittlestar's trick, the researchers say, could develop products that would be useful in computing and lithography.

"Once again we find that nature foreshadowed our technical developments," says Roy Sambles of the University of Exeter, UK, writing an accompanying analysis of the work in Nature. "But then, nature has been in the business of developing functional optical structures for a very long time."

As in billions of years. And that's just here on Earth.