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Crystal Eyes
Breakthrough in Brittlestar Vision...

The brittlestar, a relative of the starfish, seems to be able to flee from predators in the murky ocean depths without the aid of eyes. Now marine scientists have discovered its secret: its entire skeleton forms one gigantic eye.

A new study shows that a brittle star species called Ophiocoma wendtii has a skeleton with crystals that function as a visual system, apparently furnishing the information that lets the animal see its surroundings and escape harm. Now it could provide pointers to making the perfect lens, invaluable in fibre-optic communications.

The spindly arms of brittlestars may double as a primitive eye thanks to microscopic calcite crystals in its exoskeleton that focus light. These tiny lenses rival the best that human technology can offer, and their discovery solves a longstanding mystery about the behaviour of these exclusively marine invertebrates.

"This is a big breakthrough for brittlestars because no one knew how they detect light", observes Stephen Stancyk, a marine biologist at the University of South Carolina in Columbia.

Unlike their starfish cousins, brittlestars can move rapidly by walking on their arms, and they tend to avoid brightly lit places. "They're very delicate and they don't come out of their hiding places except at night because they get chewed on by lots of different animals," Stancyk says.

With the help of a scanning electron microscope, the team of researchers, from Bell Laboratories in New Jersey, found arrays of calcite crystals each about 10 to 15 micrometres in diameter, incorporated into the animal's skeleton.

These crystals were found to act as optical lenses, manipulating and focusing light. The focusing isn't random - the light appears to fall on bundles of nerves that control movement and the brittlestar interprets the surrounding light and knows whether to move or stay put.

"This is an exellent example of something that we can learn from nature," says Federico Capasso, of Bell Laboratories in New Jersey, whose colleague Joanna Aizenberg led the work, which was recently reported in Nature magazine. "These tiny calcite crystals are nearly perfect optical microlenses, much better than any we can manufacture today."

Aizenberg made her discovery by polishing a piece of skeleton and placing it on light-sensitive material used in the manufacture of computer chips.When light was shone through it it produced a pattern of spots - evidence that the crystals were acting as lenses and focusing light. The light is concentrated on a tiny spot about 5 micrometres below the bottom of the crystal. This correspondes exactly to the position of the nerve bundles in the brittlestar's body.

Approximately ten thousand spherical crystals cover the five limbs and central body - comprising one large compound eye. The vast number of lenses ensures that the brittlestar is aware of all light sources, surrounding it.

 

Orange-banded Brittle Star (Ophiothrix)

 

 

 

Brittle Star Larva

 

 

 

 

Metamorphosing Brittle Star Larva

 

 

     Visit Bell Laboratories website and read more about the research

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