Armored Slugs from the Dawn of Time

Chitons are marine molluscs. They live worldwide, in cold water, warm water, and in the tropics clinging on or under rocks, or in rock crevices. Chitons have a dorsal shell, which is composed of eight separate shell plates. These plates overlap somewhat at the front and back edges, and yet articulate well with one another. Because of this, although the plates provide good protection for impacts from above, they nonetheless permit the chiton to flex upward when needed for locomotion over uneven surfaces, and also allow the animal to slowly.

Chiton from WhidbeyIsland, Washinton. Photo by Kirl L. Onthank
Chiton from WhidbeyIsland, Washinton. Photo by Kirl L. Onthank
 Chiton belly up. Photo by californiabirdy/Getty Images

Chiton belly up. Photo by californiabirdy/Getty Images
Blue-lines chiton from Vancouver Island Photo by Jeff Rotman

Nearly all chitons are grazing herbivores. They scrape algae off of rocks with rows of teeth. Unlike mammalian teeth, which are made primarily of calcium, 160 of a chiton’s 1400 teeth are mineralised with iron. The teeth are located on a conveyor belt-like organ, the radula, with the oldest teeth at the ‘mouth’ end, and with new teeth being constantly produced to replace those worn away whilst feeding. Over its lifetime, from five to 10 years, the chiton uses tens of thousands of teeth.

Chiton mollusc's teeth magnetite Lyle Gordon NW University Evanston IL dn24329-1_800
Lyle Gordon/Northwestern University, Evanston, IL

One species, Chaetopleura apiculata, uses a crazy-looking array of teeth (pictured above) to chew up rocks and extract delicious algae. Derk Joester of Northwestern University is using the critter’s odd, self-sharpening and bulbous teeth as a model for materials that could be used to form better artificial bone. He and his colleagues have studied how organic proteins can direct and support the growth of inorganic, bony tooth minerals.

The teeth of chitons resist cracking because of the highly ordered, submicroscopic architecture that features a partnership between hard mineral crystals and fibers. The wear and crack resistance is interesting because it’s derived from an interactive foursome of carbohydrate, protein, metal ions, and mineral crystal. Magnetite mineral crystals impart the tooth with wear resistance while the carbohydrate, protein, and metal ions organize together to form long, thin fibers imbibed in the mineral crystal; the fibers impart the tooth with crack resistance.

Another scientist, David Kisailus of the University of California, Riverside, is studying a different chiton’s teeth. The gumboot chiton (Cryptochiton stelleri ) largest and most meatloaf-like of the molluscs, has an array of teeth shaped somewhat differently than its cousin’s. But it, too, grinds up rock.

Gumboot chiton belly-up Photo by Brian Good/flickr.com
Gumboot chiton belly-up Photo by Brian Good/flickr.com
Gumboat chiton teeth kisailus-images-chiton_Page_3
Gumboat chiton teeth

Kisailus has found that gumboot chiton teeth contain magnetite as well.  This mineral makes them not only super-strong, but also magnetic.

After studying the process by which magnetite is incorporated into chiton teeth, Kisalius began working on developing a similar mineralization process for materials used in solar cells and lithium-ion batteries — and, perhaps, body armor.

Chitons are armored slugs from the dawn of time, with stones for eyes and magnets for teeth. We’re lucky they’re so slow, small and harmless – I’m pretty sure they only exist as a stern warning to us all of what Mother Nature is capable of.

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