Architecture and Chemical Composition of the Magnetite-Bearing Layer in the Radula Teeth of Chiton Olivaceus (Polyplacophora)
The radula apparatus in chitons (Polyplacophora) is a toothed ribbon used to excavate algae living on and in rocky substrates. Magnetite (Fe3O4) is a component of mineralized radula teeth. It is contained in a layer beneath the surface that leads in the cutting direction. The architecture and composition of this layer in fully mineralized teeth of Chiton olivaceus were studied by scanning electron microscopy. Worn, broken, sectioned, and etched teeth were examined. Etching was done with 4N HCl or by incubating teeth in cultures of bacteria that exclusively used chitin as a source of carbon and energy.
The magnetite-bearing layer is composed of closely packed rod-shaped and elongated concavo-convex (trough-shaped) units oriented at right angles to the cutting edge making an angle with the leading surface of about 60°. Near the leading surface extensions of these units curve baseward over an angle of about 90°. During the excavating action of the radula wear predominantly occurs through fracturing along the boundaries between the elongated units. This implies that the angle between the surface of wear and the leading surface, the wedge angle, is determined by the internal structure of the tooth and is fixed at about 60°. It is discussed that the microanatomical design of the magnetite-bearing layer is such that during wear material losses are minimized.
Magnetite occurs in granular form and approximately comprises 97% by weight of the magnetite-bearing layer. Chitin is a component of the organic matrix surrounding the mineral grains and forming the boundary layer of the elongated units.
KeywordsOrganic Matrix Wedge Angle Amorphous Calcium Phosphate Outer Face Genus Clostridium
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- NESSON, M.H., and LOWENSTAM, H.A., 1985. Biomineralization processes of the radula teeth of chitons. In Magnetite Biomineralization and Magnetoreception in Organisms (ed. NESSON, M.H., and LOWENSTAM, H.A. ), pp. 333–363. Plenum Publishing.Google Scholar