Identification Photos: Chiton, Chiton sp.: The Chitons, also known as chitonase, sea cradles, loricates, coat-of-mail shells and polyplacophores, are rock-clinging marine mollusks from the class Polyplacophora and the Leptochitonidae Family, of which there are 900 to 1,000 global species. They are of great scientific interest because from fossil records they date to the Cambrian Age (over 500 million years ago).

Chitons are abundant on rocky coasts throughout the world and are found in the intertidal zone to depths of 1,200 feet. Oval in shape, they range in length from one-half inch to 12 inches, with most from 1 to 3 inches.

Chitons have bodies that are a low oval, covered dorsally with a convex, protective armor shell. The shell is made of aragonite that consists of eight linerally arranged, overlapping, calcareous plates. Note: the plates in most chitons are very visible, but in the collection shown below they are not.

The underside of Chitons consists mainly of a broad, flat foot which is used for mobility at a slow crawl and to cling to rock surfaces. Beneath the shell is a molluscan mantle, a fleshy outfolding of the body wall. The lower edge of the mantle, the girdle, extends below the edge of the shell and aids the foot in gripping.

Chitons have many gills, which are arranged in two rows within the mantle, one on either side of the body. The mouth, located on the ventral surface in front of the foot, contains a toothed, tongue-like, scraping organ called the radula. The radula has numerous rows of teeth; each row containing 17 teeth.

Most Chitons are herbivores, feeding at night on algae, but some are carnivores or omnivores. They have homing behavior and return to the same location to take shelter under rock ledges during the day. When dislodged, Chitons will roll into a ball and go with the tidal flow until they can find protective shelter. They are preyed upon by seagulls, sea stars, crabs, fish, and sea anemones.

Chiton, Chiton sp.: Collection made off a rock above the water line at Km. 21, Cabo Real, San Jose del Cabo, Baja California Sur, Mexico, April 2007. A unique collection made in mid-morning as they were out in plain sight, moving fairly rapidly back to shelter, which was about 10 meters away. Size approximately 1 inch. Identification courtesy of Greg Rouse, Scripps Institute of Oceanography, La Jolla, Calif. Description and photo courtesy of John Snow.