Scallops Have Eyes

Scallop Eyes - Dan-Eric Nilsson, Lund University

Scallop Eyes - Dan-Eric Nilsson, Lund University

For years, scallops have been gazing at the world using dozens of eyes, each of which has a segmented mirror that’s uncannily similar to those in our grandest telescopes. And scientists have just gotten a good look at one for the first time.

Yes, those scallops—the pan-seared pucks of white flesh that grace our dinner plates. Those pucks are just the muscles that the animals use to close their beautiful shells. Look at a full, living scallop, and you’ll see a very different animal. And that animal will be looking right back at you, using dozens of eyes that line the fleshy mantle on the inner edges of its shell. Some species have up to 200 eyes. Others have electric-blue ones.

Inside the eyes, the weirdness deepens. When light enters a human eye, it passes through a lens, which focuses it onto the retina—a layer of light-sensitive cells. When light enters a scallop eye, it passes through a lenslike structure, which ... doesn’t seem to do anything. It then passes through two retinas, layered on top of each other. Finally, it hits a curved mirror at the back of the eye, which reflects it back onto the retinas. It’s this mirror, and not the lens, which focuses the incoming light, in much the same way that those in segmented telescopes do.

Michael Land from the University of Sussex discovered much of this in the 1960s, by carefully eyeballing the eyes under a microscope, and tracing the path that light must take within them. He identified the mirror, he showed that it consists of layered crystals, and he suggested that the crystals are made of guanine—one of the building blocks of DNA. “It’s very impressive how Land was right about pretty much everything from some pretty simple approaches,” says Daniel Speiser from the University of South Carolina, who also studies scallop eyes. “But no one has gotten a good look at an intact mirror before.”

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