Gumboot Chiton

Today I found my first gumboot chiton, Cryptochiton stelleri (aka the great Pacific chiton, the giant Pacific chiton, or the giant Pacific fiery chiton). I've seen plenty of chiton species, but this one blew my mind.

The creature looked like a deflated football (and it was roughly the same size and shape as a NFL regulation football cut lengthwise). The gumboot chiton also looked suspiciously like a slab of liver.

The cool thing about the gumboot is its girdle, which completely covers the animal's protective plates (valves). The girdle of most chiton species covers only the edges of the eight valves.

The black katy chiton (aka leather chiton) is an exception. The girdle of this species overlaps much of the surface area of the valves, leaving only a narrow strip down the center exposed. This gives the black katy its distinctive appearance: a bold black girdle with a narrow row of "windows"--small openings that show the creature's armored plates beneath its girdle.

The gumboot is completely covered by its reddish-brown girdle. And the gumboot's thick hide feels like a football. (But the gumboot's surface, covered in algae, is also fuzzy--it feels subtly different from the leathery smoothness of a black katy chiton.)

The gumboot chiton is a creature of the low intertidal and subtidal worlds. Mainly nocturnal, it stays hidden from the sun. But on foggy days with minus tides, like today, this odd critter can turn up in tidepools.

Like all other chiton species, the gumboot uses a muscular foot to cling to rock surfaces. Though it is the largest chiton, the gumboot has the weakest grip: it is easily pried loose by waves and can wash ashore in storms.

With their segmented plates, chitons superficially resemble trilobites--arthropods that went extinct before the age of dinosaurs. Though chitons aren't related to trilobites, these mollusks are indeed ancient: they have survived more than 500 million years. What looks like a slab of liver on the beach could be a creature that has remained basically unchanged for half a billion years.

These primeval beings scrape algae from rocks with tiny teeth hardened by magnetite, a mineral attracted to a magnet. In the 500 million years that chitons have grazed algae on Earth, the planet's magnetic field has several times flipped between the north and south poles, the continents have joined together and broken apart, and countless geologic cataclysms have wiped out some species while giving rise to others. And onward the armored chitons crawl, scraping their magnetic teeth over rocks risen up from the basement of time.