Chiton Mollusks Can See With Eyes in Their Shells

Under the category of "Psst, that shell is watching you," there's a certain kind of marine mollusk, the chiton, which has evolved to embrace both protection and sight. In other words, the mollusk's shells have eyes in them. Researchers' findings on this were recently published in the journal Science.

The scientific team, from Harvard, MIT and elsewhere, says that this could help guide advances in multifunctional material design-for things like light-in-weight armor that has sensory abilities. They also looked at skill trade-offs, noting that for many animals, if two tasks are combined in the same tissue, one task usually ends up being performed more strongly than the other. Chitons, the study subjects, are the only mollusks that have living tissue within their hard shells, according to a release.

Ling Li and other researchers studied the chiton Acanthopleura granula. These creatures have lenses with mineral bases that are scattered across its armored shell. Each is smaller than a tenth of a millimeter across, the release noted.

Li noted in a statement that the eyes "allow the animal to monitor its environment with the protective armor shell. The majority of the shell is opaque, and only the eyes are transparent."

At the Argonne National Laboratory, the team performed high-resolution X-ray tomagraphy tests on individual eyes in the chiton shell, in order to find that the lenses can form images or "see." With this shell-based knowledge, the chitons can rapidly respond when predators approach. They do so by gripping onto the substrate that is below them and not allowing themselves to be dislodged from it, as the statement noted.

The study also learned that as chiton eyes increase in size and complexity, the armor actually performs less efficiently. So, the two functions of their shells need a trade-off, after all.

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