Aren’t all sea mollusks kind of weird?
Stephanie Pappas via LiveScience:
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A marine mollusk built like a tiny tank can see with eyes made of the same material as its armor.
Acanthopleura granulata is a chiton, a pill bug of the sea. This animal has a shell made of overlapping plates, which allows it to roll up in defense if a predator manages to pry it from the tidal-zone rock it calls home. Researchers have long known that chitons have soft tissue embedded in their flexible suits of armor, and that some of this soft tissue is sensitive to light. Now, they’ve discovered that A. granulata has hundreds of actual eyes that can see an 8-inch-long (20 centimeters) fish from 6.5 feet (2 meters) away.
Even weirder, these eyes are made of the same calcium-carbonate mineral as the chiton shell. However, the animal does have to trade off some structural integrity in return for the sensory function.