Polyplacophor Shells

Conspicuous Chiton Shell, Stenoplax conspicua. A representative of the Polyplacophora Class.

The Polyplacophora class is one of ten classes within the superclass Aplacophora, and this superclass is the only superclass within the phylum Mollusca. The Polyplacophora class is divided into two subclasses- Neoloricata and Paleoloricata, though only the subclass Neoloricata is represented in by living examples, the others have gone extinct.  Combined, these subclasses contain five orders, two superfamilies, and thirty-three families. As extant shells there are three orders containing twenty-five families and around 600 species. Shells in this class first appeared in the late Cambrian Period. Some early fossil species only had seven plates. Shells in the Class Polyplacophora are commonly called Chiton (pronounced kite-on) shells, or Polyplacophorans.

 The name Chiton comes from the Greek word meaning frock, tunic, or coat-of-mail. Coat-of-mail refers to chain mail armor, which emphasizes the armor plated nature of these shells. The word Polyplacophora means “bearing many plates”. Shells in this class are made up of eight separate overlapping plates, called valves. The underside and ends of the valves are attached to a tough mantle which covers the rest of the animal.  This armor plating provides excellent protection,  while being flexible enough to allow the animal to mold and attach itself to irregular hard surfaces. Chiton Shells have a reduced head, with no eyes or tentacles. They do have a chemosensory organ that extends out of the mouth to sense the environment. Polyplacophorans range in size from 0.8cm (0.3 inches ) to 33 cm (12.9 inches) in length.

Chitons of the class Polyplacophora are found attached to hard surfaces, in marine environments. They live intertidally, and to depths exceeding 7,000 m (23,000 feet). They are found worldwide in temperate to tropical seas. Most species are herbivores that rasp algae off the rocks by use of their radula. One genus is predatory and feeds by trapping small invertebrates under their mantle.

Humans have made limited use of Polyplacophorans, with only one species being widely used as a food source by indigenous people. Today, a few species are harvested commercially as a food source.

One Chiton Shell of the Ischinochitonidae Family of Ischnochiton Shells  can be found in this website:

Conspicuous Chiton Shell, Stenoplax conspicua

Two Chiton Shells of the Chitonidae Family of the True Chiton Shells can be found in this website:

White-striped Chiton Shell, Chiton albolineatus

Sea Cockroach Shell, Chiton articulatus