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Chitons, also called polyplacophorans and rarely polyplacophores, are 600 species of molluscs of the Class Polyplacophora. They glide slowly in the intertidal zone using their muscular feet.

Lined Chiton (Tonicella lineata)

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Structure The calcareous armour shell that chitons carry dorsally are protective and made of aragonite. The shell is divided into eight plates (also called valves).

Ventrally, a chiton's body is surrounded by the girdle, the ventral extension of the shell. Between the body and the girdle, there is a mantle cavity[?], connected to the outside by two water channels. The one on the side is the incurrent water channel. The one attached to the anus is the excurrent water channel. The majority of the body is a snail-like foot. There is a head that contains a mouth with a razor-sharp tongue called the radula. The half near the anus has gills. [1] (http://www.animalnetwork.com/fish2/aqfm/1999/aug/art0801/wbfig1.jpg)


Black Chiton (Katherina tunicata) on a stone with a seastar

Its English name originates from a Greek word chitōn, which means "tunic[?]". Its Greek-derived name Polyplacophoran comes from the words plako- (tablet) and -phoros (bearing). The Class Polyplacophora was named by J. E. Gray in 1821. Chitons were also called Cyclobranchians (round arm) in the early 19th century.

Activities Chitons eat algae, and sometimes bacteria, with their radula.

Predators include seagulls, seastars, crabs, fishes and sea anemones.

Classification Classification method I [2] (http://www.schnr-specimen-shells.com/Polyplacophora):

  • Class Polyplacophora
    • Order Neoloricata
      • Family Leptochitonidae
        include genus Leptochiton
      • Family Afossochitonidae
      • Family Ischnochitonidae
        include genera Callistochiton, Callochiton, Chaetopleura, Ischnochiton, Lepidochitona, and Lepidozona
      • Family Mopaliidae
      • Family Chitonidae
        include genus Chiton
      • Family Cryptoplacidae
      • Family Acanthochitonidae
        include genera Acanthochitona, Notoplax
      • Class Monoplacophora
      • Order Tryblidiida
      • Family Neopilinidae
      • Family Vemidae
      • Family Monoplacophoridae
      • Family Laevipilinidae
The following classification is Parker, S. P. [3] (http://www.worldwideconchology.com/Chitonidae.htm):
  • Class Amphineura
    • Sub-class Polyplacophora
      • Order Neoloricata
        • Suborder Lepidopleurina
          • Family Hanleyidae
          • Family Choriplacidae
          • Family Lepidopleuridae
        • Suborder Ischnochiyonina
          • Family Subterenochitonidae
          • Family Ischnochitonidae
          • Family Schizoplacidae
          • Family Callochitonidae
          • Family Callistoplacidae
          • Family Chaetopleuridae
          • Family Mopaliidae
          • Family Schizochitonidae
          • Family Chitonidae
        • Suborder Acanthochitonina
          • Family Acanthochitonidae

Chitons were divided into Chismobranchians and Polyplaxiphores in the early nineteenth century.


Gumboot Chiton (Cryptochiton stelleri)

The largest chiton is the pink gumboot chiton of the Pacific Northwest. [4] (http://www.alaska.net/~scubaguy/images/gumbootchiton.jpg)

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