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The Shells Have Eyes

Most of us only know that scallops are just one of the delicacies the sea can offer us. But did you know that these scallops have eyes? They have up to 200 eyes, to be exact, and these eyes function like telescopes. A new study has revealed that these eyes, like ours, dilate and contract in response to light.

“It's just surprising how much we're finding out about how complex and how functional these scallop eyes are,” says Todd Oakley, an evolutionary biologist at the University of California, Santa Barbara.
The optics of scallop eyes are set up very differently than our own ocular organs. As light enters into the scallop eye, it passes through the pupil, a lens, two retinas (distal and proximal), and then reaches a mirror made of crystals of guanine at the back of the eye. The curved mirror reflects the light onto the interior surface of the retinas, where neural signals are generated and sent to a small visceral ganglion, or a cluster of nerve cells, whose main job is to control the scallop's gut and adductor muscle. The structure of a scallop's eye is similar to the optics systems found in advanced telescopes.
For many years, the physics and optics of the scallop eye posed a perplexing problem. "The main retina in the eye gets almost completely unfocused light because it's too close to the mirror," says Dan Speiser, a vision scientist at the University of South Carolina and the senior author of the new study. In other words, any image on the proximal retina would be blurry and out of focus. “That just seems so unreasonable to me,” Speiser says.
The new study sheds some light on this mystery. The researchers found that the scallop pupils are able to open and contract, though their pupillary responses aren’t as quick as our own. A scallop pupil's diameter changes by about 50 percent at most, and the dilation or contraction can take several minutes. Their eyes don’t have irises like our eyes do, and instead, the cells in the cornea change shape by going from thin and flat to tall and long. These contractions can change the curvature of the cornea itself, opening the possibility that the scallop eye might change shape and respond to light in a way that makes it possible to form crisper images on the proximal retina.

The scallops’ many eyes tell us a lot about the evolution of eyes in organisms, and the scallop is not the only sea creature that have weird eyes.

Find out more on Smithsonian.

(Image Credit: Science Magazine / YouTube)


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