BIOMINERALIZATION PROCESS OF MAJOR LATERAL TEETH OF JAPANESE CHITON, ACANTHOPLEURA JAPONICA

Chitons are well-known as unique marine molluscs which have specific teeth containing magnetite (Fe3O4) as a major component.  Iron is located in the second lateral teeth which are used for scraping and makes the teeth much harder other marine molluscs.  There are about 80 pairs of the teeth on a radula of Japanese chiton Acanthopleura japonica, which keep a sequence of maturation with varying their appearance, hardness, and constituents.  In order to elucidate this transition process from the materials scientific point of view, XRD, XMA, and micro-XAFS techniques were applied to the teeth of chiton, Acanthopleura japonica.
From those results, the maturation process of the teeth could be divided into 5 stages as follows. At the earliest stages, organic frameworks are constructed without any mineral component (stage I).  In the next stage, reddish-brown amorphous Fe(III) compound is accumulated into the tooth margin and the posterior part (stage II).  The reddish-brown teeth exist in two or three rows and then magnetite formation starts abruptly in following teeth rows.  The colour of posterior part and tooth margin turn into black, and the anterior surface shows grey colour for about 10-15 rows (stage III).  In next teeth row, the colour of anterior surface changes into yellowish-red suddenly and obviously (stage IV). Mineral phases of the teeth also increase in stage IV; amorphous calcium phosphate intrudes into the anterior part gradually, and goethite (a-FeOOH) and lepidocrocite (g-FeOOH) appear as minor iron components.  At final stage of the maturation, the teeth get thickened and fully mineralised with these inorganic compounds and abundance of magnetite is about 70% against total iron compounds (stage V).
The tooth formation in Chitonida and Cryptochiton has been investigated (Lowenstam 1989), however, that of Japanese chiton Acanthopleura japonica is different from them and more complex with stage III described above.  This result suggests that magnetite formation might occur with spatiotemporally independently from those of other minor iron components in the tooth.
Reference: H.A. Lowenstam and S. Weiner, On Biomineralization, Oxford University Press (1989).

[ home   ] [ beginning ] [ page 2 ]  [ invited lecturers  ]  [ communications  ] [ pictures  ] [  previous  ]  [ next ]