Chitons are well known to have special strong teeth accumulating iron oxides, especially magnetite (Fe3O4), and calcium phosphates as major components. In the case of Japanese chiton Acanthopleura japonica, about 80 pairs of the iron teeth (ca. 400 x 200 x 500 mm3) locate on a radula with their maturation sequence which can be divided into five stages from their mineral composition and appearance. The teeth was soft with organic flame work consist of chitin in the first maturation stage, and their color turns into reddish-brown with amorphous iron (III) components in the flame at the second stage. The posterior edge of a tooth where is main place for feeding accumulates magnetite abruptly at the thierd stage, and its abundance of magnetite increased until 60th teeth on a radular teeth, the fourth stage. Other mineral components can be observed in the later maturation stages; at third stage with red color, goethite (α-FeOOH) and lepidocrocite (γ-FeOOH) are stored at posterior surface of the tooth, and finally the posterior part of the tooth is filled with hydroxyapatite (Ca10(PO4)6(OH)2) at final maturation stage. The hardness of the teeth was much higher than those of other marine creature at intertidal zone because of the magnetite.
In this study, nano-indentation technique was applied in order to evaluate of the mechanical property of the teeth of chiton and their variation through the teeth maturation on a radular teeth. Meterial scientific properties of the teeth of chiton has been investigated with ICP-AES, EPMA, FE-SEM, X-ray diffraction, IR, Mossbauer, Raman and X-ray Absotption spectroscopy.