Hubble in a bubble: Scallop eyes act like tiny telescopes

Hubble in a bubble: Scallop eyes act like tiny telescopes
    Under the sea, vision can get weird.
    Cuttlefish have W-shaped pupils
    and mantis shrimp see many colors we don’t,
    but scallops have one of the weirdest visual systems of all.
    These marine creatures have up to 200 eyes, and each of them uses a mirror,
    instead of a lens to focus light.
    Researchers put these eyes under the microscope, and found some amazing things.
    The mirror is made from crystals of guanine.
    You may be more familiar with its role in DNA,
    but crystalline guanine is also a highly reflective material
    that can be seen everywhere in nature, from fish scales to chameleon skin.
    Guanine crystals typically form into bulky prisms,
    but the crystals in the scallop’s eye,
    form into perfect squares.
    Like a telescope mirror, the scallop’s tiled squares create a smooth surface,
    which minimizes optical aberrations.
    The shape of this mirror is also the key to unlocking another mollusk mystery.
    The scallop actually has two retinas, the upper retina and the lower retina.
    The upper retina cells fire when a shadow crosses over the scallop,
    indicating a potential predator attack,
    and tell the scallop to escape.
    But scientists were unsure of what exactly the lower retina did.
    Using simulations, the researchers were able to infer
    what happens when light hits the mirror.
    These calculations suggested that the bottom retina provides peripheral vision in dim light.
    Of course, 200 eyes receiving light from an area only a few inches across
    would produce a lot of overlap.
    The researchers hypothesize that there may be some process in the scallop’s ganglion
    that combines this information overload into a single cohesive image.
    But until we know how their “brain” works,
    the scallop’s eye will still be one of many weird optics,
    found beneath the sea.
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