I was in Seattle over Memorial Day weekend for a wedding, and there was a minus tide Monday morning. I couldn’t resist a chance to see some of the creatures that live in this most beloved habitat of mine. Seattle has a few spots to go tidepooling, but the one closest to where I was staying is Golden Gardens Park. The tide wasn’t that low, so conditions weren’t ideal, but my husband and I saw a bunch of cool stuff nonetheless, including some of my favorite mollusks, chitons! Here’s one of the ones we saw.
I’m going to focus on chitons in this post because there’s some cool chiton news as of late: Chiton eyes! The extra cool thing: they are made of rock, aragonite in particular. They also seem to do more than just sense light and dark: in laboratory conditions, it seemed the chitons can perhaps tell the difference between threatening darkness from a predator’s approach as opposed to darkness caused by a cloud momentarily blotting out the sun. Also cool is that the eyes work either underwater or in air. That seems pretty handy if you happen to be living in the intertidal zone.
Chitons are not the only creatures with rock eyes. Trilobites had rock eyes too. Trilobite eyes were also made of calcium carbonate crystals, but a different crystal formation, namely calcite. Chitons are the first organisms discovered to have aragonite for their rock eyes.
The chitons we saw were mossy chitons, which I believe don’t have eyes, but they fascinating anyway. Here’s another that we saw.