This Mollusk's Exoskeleton Is Covered in Hundreds of Tiny Eyes

Let's build armor that can monitor its own integrity, just like the chiton can.

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Nov 19 2015, 7:00pm

A gif illustrating where the West Indian fuzzy chiton's eyes are. Image: Carla Schaffer/AAAS

Fiction is filled with wild concepts for smart body armor and architecture, from Dune's watertight stillsuits to Ant-Man's shrinkable duds. But the intertidal mollusk Acanthopleura granulata, also known as the West Indian fuzzy chiton, may have them beat with its bizarre eyeball-adorned armored shell, described in new research published today in the journal Science.

This extraordinary mollusk has managed to finagle an evolutionary compromise between two adaptations that would seem to be mutually exclusive—sight and defense. While its hard outer shell protects the mollusk's soft insides from predators, it is also decked out with hundreds of microscopic, mineral-based lenses that can resolve images of incoming attacks.

"It is sacrificing mechanical protection to some extent, but providing a completely different function to the system, so that the animal can see the potential predators close by," Ling Li, a Harvard biomimetics expert and co-author of the study, told me over the phone. "This will increase the overall defense performance."

Acanthopleura granulata. Image: Hans Hillewaert

To put in Skyrim terms, the chiton gets a bonus for mix-and-matching the powers of both light and heavy armor, as opposed to limiting itself to one or the other. It is able to strike this balance by building its lenses from minerals—primarily aragonite crystals—instead of proteins, which are the basis for most eyes in the tree of life, including our own. Manipulating the refractive properties of these crystals allows A. granulata to monitor its surroundings while ensuring that its visual organs are not as vulnerable to injury as those of other animals.

"This animal is very slow," Li told me. "It cannot just run away. The only thing it can do is clamp down onto the rock so that predators cannot eat it. Once they are clamped down, it is actually very difficult to dislodge them."

This dual-use armor is fascinating on its own merits, but it also has implications for engineering smarter body armor, vehicles, and buildings.

"Perhaps one day people might develop a 3D printer which can print ceramic materials with mechanical strength, but also embed sensory elements inside those structural elements," Li suggested. "By doing this, the materials will be able to maybe send signals to the user to monitor the structural integrity, or the environment."

For instance, he said, take airplane wings. "They are constantly subject to fatigue, and there are a lot of micro-damages going on in an airplane wing. How do you monitor the structural integrity in real time?"

"If you can embed some sensory elements in those structures similar to the chiton, you can monitor the structural health of the system," Li told me. "That would be a great benefit. The material becomes smarter."

Replicating the chiton's ocular armor artificially, however, will be no easy feat, and Li said we are still "several steps away" from being able to integrate it into modern technologies. But regardless, the fact that this unassuming-looking mollusk might inspire sensory airplanes is a reminder that nothing can meet stringent design parameters more creatively than evolution.

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