Creature Feature: Gumboot Chiton

Even though MSI’s aquarium is located along the shores of SF Bay, we are also home to a variety of different animals from the rocky shores of the Pacific Ocean. We collect these animals from Pillar Point, on the north end of Half Moon Bay. Life in the tidepools is pretty different from life in an estuary, like SF Bay – the water is colder and saltier, the waves rougher, and the shoreline more rugged. Animals that live here need to be prepared for almost anything: heavy storms, hot sun, low tide, high tide, and predators.


One of my favorite tidepool animals is a funny looking cousin of snails called the gumboot chiton (Cryptochiton stelleri). The gumboot chiton is the largest of the half-dozen or so species of chiton you can see along the rocky shoreline in California. It can grow to 14 inches long! Just like a snail, it has armor to protect itself – but a chiton’s armor is in the form of 8 bony plates rather than one hard shell. You might find these plates on the beach occasionally – they look a bit like butterflies. On some chitons the plates are visible, but a gumboot chiton is covered with bumpy, reddish-brown skin. It looks a bit like a football.


Chitons are vegetarians and spend their time slowly moving along the rocks, scraping up algae (seaweed) with a rough, tongue-like organ called a radula. They breathe through gills, which are spiral-shaped and lay up against both sides of the chiton’s large foot.


Chitons hang on tight to the rocks in the lower intertidal or subtidal areas of the rocky shore – this means you will usually only see them out of the water at the lowest tides. But they don’t hang on as tightly as other chitons, so they sometimes get knocked loose by strong waves and washed into higher areas of the tidepools.

The next time you’re at Pillar Point or another rocky coast area, be on the lookout for these slow-moving, mild-mannered mollusks!


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