Calcium biomineralization in the radular teeth of the chiton, Acanthopleura hirtosa.

A method has been devised for isolating the calcium biomineral from the iron biominerals and organic components present in the major lateral teeth of the chiton Acanthopleura hirtosa. Fourier-transform infrared spectroscopy of the calcium biomineral indicated that it was an apatite material containing carbonate and fluoride ions. Carbonate was not found to be present as a separate phase. The apatite was further separated into low and high density fractions, both of which showed crystallinity intermediate between that of bovine tibia cortical bone and human tooth enamel, as indicated by powder X-ray diffraction analysis. The calcified region of the major lateral teeth was also studied in situ using transmission electron microscopy and electron diffraction analysis, revealing a close spatial relationship between the mineral apatite phase and underlying organic matrix. It is suggested that the architectural arrangement of apatite biomineral and fibrous organic constituents imparts specialized mechanical properties to the tooth making it ideally suited for the task of obtaining food from hard surfaces.