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Chiton

Along my home California coast, you may find, on the softest littoral rock, an infinite number of subtle dimples. It’s as if, for eons, some ambitious soul lingered to rub first this spot, then that, until each became a smooth and nearly uniform divot. These shallow holes—catching seawater, reflecting sky and fog—are not the work of some invisible thumb, however, but of the foot of a five-hundred-million-year-old: a mollusk. They are the resting places of chiton.

Now the best way to understand a chiton (kī-tän) is to wait until sunset, flop on your belly at the sea’s rocky edge, and lie quite still. Make sure it’s high tide, when chitons are busiest. Then, with your ear pressed to the stone, you might hear the faint vibrations of scraping as, underwater, their rasp-like radulae rev up in their mouths and they begin to lurch forward to graze the algal fields, inch by inch. Some chitons reap “diatom scuzz”; others prefer a healthy leaf of algae. All cut with precision: The outermost “teeth” of their radulae are capped with magnetite, harder than stainless steel.

Chitons are also called “sea cradles,” because eight calcareous plates overlap across their backs, a defensive arch surrounded by a fleshy girdle. More than nine hundred species crawl the world’s shores, but they’re most varied on our West Coast (and in Australia). If you’re lucky, while perusing a Pacific tide pool you might chance upon a foot-long brick-red gumboot chiton, a creature lovingly nicknamed the “wandering meatloaf.” This giant’s leathery girdle actually wraps clear around its plates and is slightly fuzzy to the touch: Twenty species of red algae grow on its back. All of which makes me wonder if the gumboot wouldn’t enjoy nibbling on itself, just a little.

Chitons are guarded, territorial. They don’t like limpets, another grazer. They have light-sensitive organs, “aesthetes,” in their shells—their plates are innervated—which relay signals to the region resembling a head. Some even have lens-bearing “eyes” on their backs and see shapes. Thus, when your shadow crosses, a chiton will cling fast, masquerading as rock. Should you, or a wave, catch and flip a chiton upside down by surprise, however, it will curl into a tectonic ball and go with the flow, tumbling to safety.

But this is why it’s really worth lying on your stomach: Each night, some chiton species creep forward on established trails to their feeding grounds, usually no more than a few feet from their primary dimple. Out and back, they go, harvesting, and by morning return on these mucal routes to their hammocks in the stone, where they seal tight to conserve moisture. They perform these rounds for months before moving on to fresh algal pastures. Do you hear them? No one knows how they navigate, exactly, nor how they scour their pits (and some species don’t). Like limpets, their secretions may dissolve the stone, before they polish off the job with their teeth. But now, again, I find myself wondering: Is the chiton’s home its groove, equally a rut and a cradle? Or is it the endless forays made from this center?