MATRIX HETEROGENEITY IN THE RADULAR TEETH OF THE CHITON ACANTHOPLEURA-HIRTOSA

The structure and organization of the organic matrix of the cusps-of t he major lateral teeth of the chiton Acanthopleura hirtosa have been e xamined using conventional light and transmission electron microscopy techniques and by using the protein ferritin as an ultrastructural pro be. The results show major structural differences in the organic matri x between the surface layers of the anterior (calcified) region and th e posterior (magnetite-mineralized) region and their respective underl ying regions. In addition, the central (lepidocrocite-mineralized) reg ion of the tooth has been examined and shown to consist of bundles of fibres arranged such that they display a tightly interwoven pattern. I t is suggested that while the structural organization of surface fibre s readily permits the passage of ions required for mineralization, the architecturally discrete distribution of biominerals found in mature chiton teeth is due mostly to spatial delineation of the tooth by matr ix macromolecules in the central region of the tooth.