Chitons are mollusks belonging to the class Polyplacophora. They are mostly flattened with eight dorsal, limy plates. This is where they get their class name from. (Polyplacophora means “bearing many plates.”) These plates overlap posteriorly and are typically dull in color to blend in with their surroundings (though this is not always the case). Most chitons rarely grow larger than 5 cm and the largest rarely ever exceed 30 cm. They’re usually found stuck onto rocky surfaces in the intertidal zone, but some have been found at much greater depths. If a chiton gets detached from its rock, it can roll up like an armadillo for protection.
Shown is the mossy chiton (Mopalia muscosa), whose mantle is covered in defensive hairs and bristles.