Sea Discovery: Chitons, the algae vacuums of the intertidal

Chitons are a group of molluscs that are defined by the eight plates that act as armour on their backs. These plates are mobile and allow the oval-shaped mollusc to curl itself into a ball when hiding from predators (just like wood bugs in your backyard). After chitons die, their plates, which are made up of calcium carbonate, often wash up on shore and resemble butterflies with their curved shape.

A gumboot chiton (Cryptochiton stelleri) curls up as a defence mechanism, protecting its soft underparts. Photo: Jerry Kirkhart

Like some of their mollusc cousins, such as limpets and whelks, chitons use their muscular foot to suction themselves to rocks and move. As they move along, they scrape algae with their radula.

Two mossy chitons (Mopalia muscosa) occupy a crevice during the day, waiting for the water to rise and darkness to move. Photo: Peter D. Tillman

Mossy chitons have a unique appearance with their “mossy” looking girdle that has long, stiff hairs. These fuzzy-looking chitons are often found in the intertidal and are very particular about when they like to move from their settled position. Only when it is dark and wet, or they are underwater, do these slow-moving molluscs begin their feeding mission.

Another chiton that is nearby is the gumboot chiton or giant Pacific chiton. This species is the largest chiton in the world! The gumboot chiton can grow up to 35 cm has a bumpy, reddish-brown girdle that completely covers its backplates. These massive molluscs were an important food source and are culturally significant for many First Nation peoples along the coast of British Columbia.

References & Resources

Mossy Chiton, Mopalia muscosa. Central Coast Biodiversity. Kelly Fretwell and Brian Starzomski (2013).

Giant pacific chiton, Cryptochiton stelleri. Central Coast Biodiversity. Kelly Fretwell and Brian Starzomski (2013).

Harbo, Rick M. Whelks to whales: coastal marine life of the Pacific Northwest. Harbour Publishing Company, 2011.


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