On November 24th, 2015 we learned about

Molluscs’ armored eyes are made of minerals

If you’ve poked around tide pools at the shore, you may have seen some small, rocky looking creatures stuck to the rocks called chitons. Surprisingly, they may have also seen you, despite being completely covered in a hard layer of ceramic armor. In an amazing display of anatomical compromise, Acanthopleura granulate have evolved to grow hundreds of eyes not covered by, but made of the same minerals that comprise their protective shells. The eyes themselves aren’t really suited for detail or distance, but they do enable to the plated mollusk to keep it’s guard up without exposing any sensitive tissues.

An eye for danger

The eyes on A. granulate are extensions of its armor in more ways than one. As algae-eaters who spend all day clinging to rocks, they’re not using their eyes to hunt anything down the way a mobile predator does. The array of eyes sprinkled across the animal’s shell instead allow it to see oncoming danger and increase the grip on its rock to avoid being pecked or pried off. The eyes themselves are slightly less rugged than the opaque shell, which is likely why they’re located in indentations between the thicker plates of armor, almost like your cheekbones and eye sockets protect your (much squishier) eyeballs in your head.

While some animals have light-sensitive membranes on their bodies, it’s important to note that these are actual eyes made of mineral, capable of forming an image of the local environment. Structural analysis has found that they should be able to see a fish’s movement up to six feet away. While that image would be blurry, it would be enough to warn the chiton of impending nibbles. On the plus side, the optics of these eyes would function equally well both underwater and in the air, allowing the chiton to stay safe both at high tide and low tide.

Shielding our sightlines

This combination of traits has material scientists excited. While most human applications would demand higher clarity than a blur at six-feet, the chitons’ eyes might inform us when designing future protective lenses and windows, such as in military applications. It’s another opportunity for biomimicry, learning new techniques that evolution has already iterated on in ways we weren’t expecting.

Source: Armor plating with built-in transparent ceramic eyes by David L. Chandler, MIT News

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