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Marine eye to future
Finding on creature may aid optical networks
By Gareth Cook, Globe Staff, 8/23/2001
CREATURE FEATURE Scientists say brittle stars are covered in tiny 'eyes'.
starfish-like creature found in coral reefs from Bermuda to Brazil is covered with thousands of tiny crystal lenses, scientists have found, making it the only known animal that is basically a living eye.
The optics of the brittle star, a fast-moving reddish-brown sea creature the size of a human hand, may even help shape the future of the Internet, researchers say.
The discovery, reported in today's issue of the journal Nature, solves an old paradox: Researchers knew the animal could see, but they couldn't find its eyes.
They discovered that the animal's external skeleton is embedded with thousands of tiny lenses, each about one-twentieth of a millimeter in diameter.
''Basically, this animal is one giant compound eye,'' said Sonke Johnsen, an assistant scientist at the Wood's Hole Oceanographic Institution. ''It is as if we were seeing through our bones.''
The design of the brittle star's tiny lenses, developed over millions of years of evolution, is so exquisite that researchers think it could inspire better components for the optical networks that send torrents of data, carried on beams of light, around the world.
''This primitive organism forms a material with unique optical properties,'' said Joanna Aizenberg, a research scientist at Bell Laboratories-Lucent Technologies, who led the team. ''Here, nature teaches us a lesson in how to solve a very complex technological problem.''
Scientists said it would by very difficult to imagine how the world might appear to a creature covered in fields of tiny eyes, all moving on one of that animal's five undulating arms. But the species of brittle star in the study, Ophiocoma wendtii, is able to see well enough to ''quickly escape from predators into dark crevices,'' they wrote.
The team combined a number of clues to show that the animal sees through its skeleton. In the wendtii, but not in other closely related species that do not seem to respond to light, they saw spherically shaped nodules, made out of a substance called calcite, in the skeleton.
At Bell Labs, the team placed a piece of the skeleton on a substance that is sensitive to light. When a light was sent through the skeleton, the team found a series of bright dots, evidence that the nodules had been acting as lenses.
A more detailed optical analysis of the nodules found that they were perfectly designed to bring in light, and to focus it sharply on a point. And when they looked at the focus points of the nodules, they found bundles of nerves, presumably to send along the visual information, much as the optic nerves of humans do.
With the rise of the Web, engineers at Bell Labs and other communications research laboratories have been racing to find better ways to move pulses of light, which carry information through large trunks of fiber optic cable. One technology, ''microlens arrays,'' gives them the ability to process many streams of light at once, redirecting them as needed.
The brittle-star microlenses are impressive, Aizenberg said, because they are globe-shaped, rather than thin like the lens of a magnifying glass, yet they can focus light without too much distortion.
Gordon Hendler, one of the paper's authors and an expert on brittle stars with the Natural History Museum of Los Angeles County, said his interest in the animals began decades ago, when he noticed that they appeared different in the day than at night.
At night, the animals appear blackish-brown and pale gray. In the day, though, pigmented cells move up and over the lenses, decreasing the amount of light that hits them, and serving as ''sunglasses,'' he said.
These kinds of adaptations are common, said Johnsen, the Woods Hole scientist, who studies how marine animals take in and process light. He said that squid's eye, for example, is 15 inches in diameter, and that there is a species of shrimp whose eye has receptors sensitive to 12 different wavelengths of light, compared with just three in humans.
Aizenberg said the team was also stunned at how the brittle star has been able to adapt material to two uses at once - as a protective armor and as a crystal that allows tiny beams of light to shine in, painting a picture of the world around it.
''This is why we say nature is ahead of us,'' Aizenberg said.
This story ran on page A1 of the Boston Globe on 8/23/2001. © Copyright 2001 Globe Newspaper Company.
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