STRUCTURAL ORGANIZATION OF THE CUSPS OF THE RADULAR TEETH OF THE CHITON PLAXIPHORA-ALBIDA

The structure, morphology and organisation of the cusps of the major l ateral radula teeth of the chiton Plaxiphora albida have been examined using light, transmission and scanning electron microscopy, together with energy dispersive X-ray analysis and Mossbauer spectroscopy. In t his chiton species, both the anterior and posterior surfaces of the ma jor lateral teeth are composed of magnetite, which is indicated to be non-stoichiometric and associated with some maghemite, together with s mall amounts of phosphorus and silicon. This outer layer surrounds an inner core region of the tooth, which only reaches the surface through a small window zone on the anterior surface and which contains large amounts of iron and phosphorus presumably in the form of iron(III) pho sphate. The organic matrix, on which the teeth are constructed, consis ts of a zone of densely packed fine fibres at the surface of the tooth , underlain by larger fibres which become sparser deeper into the cusp . The core region is characterized by the presence of densely packed s hort fibres. In contrast to the situation found in most other species of chiton, large fibres of the organic matrix extend throughout the re gion of magnetite mineralization, leading to the suggestion that the m atrix exerts more control over the mineralization of magnetite than ha s previously been thought. (C) 1997 The Royal Swedish Academy of Scien ces.