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A dorsal view of a chiton, showing the eight shell plates. Chitons are small to large, primitive marine mollusks in the class Polyplacophora. There are 900 to 1,000 extant species of chitons in the class, which was formerly known as Amphineura. Chitons have a shell which is composed of eight separate shell plates or valves. These plates overlap somewhat at the front and back edges, and yet the plates articulate well with one another. Because of this, although the plates provide good protection for impacts from above, they nonetheless permit the chiton to flex upward when needed for locomotion over uneven surfaces, and also the animal can slowly curl up into a ball when it is dislodged from the underlying surface. The shell plates are surrounded by a structure known as a girdle.

Chiton (Dorsal)

A dorsal view of a chiton, showing the eight shell plates. Chitons are small to large, primitive marine…

A ventral view of a chiton, showing p, foot; o, mouth; kr, oval fringe; and br, the numerous ctenidia. Chitons are small to large, primitive marine mollusks in the class Polyplacophora. There are 900 to 1,000 extant species of chitons in the class, which was formerly known as Amphineura. Chitons have a shell which is composed of eight separate shell plates or valves. These plates overlap somewhat at the front and back edges, and yet the plates articulate well with one another. Because of this, although the plates provide good protection for impacts from above, they nonetheless permit the chiton to flex upward when needed for locomotion over uneven surfaces, and also the animal can slowly curl up into a ball when it is dislodged from the underlying surface. The shell plates are surrounded by a structure known as a girdle.

Chiton (Ventral)

A ventral view of a chiton, showing p, foot; o, mouth; kr, oval fringe; and br, the numerous ctenidia.…

An illustration of the dorsal view of a chiton with the shell removed. Showing b, buccal mass; ov, ovary; od, oviduct; i, coils of intestine; ao, aorta; c' keft testine; and c, ventricle.

Chiton with Shell Removed

An illustration of the dorsal view of a chiton with the shell removed. Showing b, buccal mass; ov, ovary;…

An illustration of a pallial eye and aesthetes of a chiton.

Pallial Eye

An illustration of a pallial eye and aesthetes of a chiton.