Sea creature with 100 eyes

If you spot a West Indian fuzzy chiton, it has most likely spotted you too.

Chitons may lack a brain, head and eyes in the classic sense, but nestled in the shell of this primitive marine mollusc are hundreds of tiny ‘eyes’, complete with lenses that focus light to create images. The finding was reported in Science in November, by Matthew Connors and his colleagues at the Massachusetts Institute of Technology.

“Every single one of these funny little lenses works as a reasonably good camera,” says Duke University biologist Sönke Johnsen.

The chiton’s multiple eyes could inspire more robust robot vision systems, Connors says.

Oval in shape and just under the size of a credit card, chitons spend their days crawling along rocks, camouflaged and shielded by their brownish-grey armour.

Their tiny eye-like structures – a unique feature among molluscs – were noticed by 19th century biologists. They assumed that these eyes, more correctly called aesthetes, would only be capable of telling light from dark.

But in 2011, Johnsen and his colleagues discovered chitons could distinguish objects.

Chitons quickly clamped down on their rocks when a dark fish-shaped object was placed above them. But when the researchers dimmed the lights by the equivalent amount, the chitons didn’t flinch.

The Connors team decided to take a closer look. The chiton’s eyes consist of a tough crystal lens positioned above a small cluster of photoreceptor cells. The team extracted the lenses, then rigged up a microscope to act like a slide projector, with the chiton’s eye acting as the projector’s lens. When they shone images through this lens, the images were a thousand times fuzzier than the image a human eye lens would cast, but still recognisable – and much sharper than Connors was expecting.

Why a chiton needs so many eyes remains a mystery. The chiton ‘brain’ is a rudimentary cluster of nerve cells with insufficient power to integrate the signals from hundreds of eyes. Chitons “make a goldfish look like Albert Einstein!” says Johnsen. “It’s like having a whole row of television sets on when no one’s watching.”

Johnson and Connors suspect the reason chitons have so many eyes comes down to their tough lifestyle on the waterfront. Chitons are battered by breaking waves, and their eyes are frequently damaged – but they have plenty of spares, suggests Connors.

Could the tough, yet perceptive, chiton be inspiration for future robot designs? Johnson thinks so. Mars exploration rovers now carry a few cameras on masts. Instead, they could carry hundreds of tiny cameras, ready to fill in for each other should a few of them get cracked or covered by dust, he suggests.

“If you can build a robot like that, it’ll be really robust,” Johnson says.

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