See Creature

Biologists discover eyes--lots and lots of eyes--in brittle starfish

02-01-2002 // Mark Cheater

WHEN IT COMES to spotting predators, one brittle star is all eyes. Literally. The five limbs of Ophiocoma wendtii, a spindly relative of the starfish, are covered with hundreds of tiny lenses that allow the creature to see approaching enemies.

Brittle stars lack the large, specialized eyes that many animals possess. But biologists have long noted the ability of some brittle star species to react to light and avoid predators. O. wendtii, common in the Caribbean, changes its color at night and moves to dark crevices when threatened.

How does it manage this without eyes? Alexei Tkachenko and Joanna Aizenberg at Lucent Technologies' Bell Labs and colleagues in Israel and California recently found that tiny calcite crystals in the brittle star's external skeleton focus light onto nerve bundles in the creature's body. The array of crystal lenses may act like crude versions of the compound eyes possessed by insects. "Nature is full of surprises," says Aizenberg. "Our finding solves the mystery of how these creatures are able to detect predators in spite of lacking traditional eyes."

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