The physical structure and mechanisms of biomineralizatìon have been elucidated in the major lateral teeth of the chiton genus Acanthopleura with the aid of light and scanning electron microscopy and energy dispersive spectroscopy. Following its recent revision, this genus currently consists of 15 species, including three species suppressed as synonyms. Specimens representing all 18 (nominal) species have been examined. With two exceptions, the major laterals are typically discoid and unicuspid with only limited interspecific variation. The teeth of A. loochooana are also essentially discoid but have a small, distinct distal indentation, while those of A. rehderi possess four short rounded denticles. Biomineralization in all species of Acanlhopleura occurs in architecturally discrete compartments and, with the exception of A. rehderi, is consistent in all tooth regions except the cusp core, where A. curtisiana, A. miles, A. araucariana and A. loochooana differ in having substantial amounts of iron. The first three of these species were previously included in the genus Squamopleura and there is evidence to suggest that this genus should not have been suppressed. The substantial difference in tooth structure between A. rehderi, with its four denticles and total lack of a lepidocrocite region, and that of other members of the genus Acanthopleura suggest that this species may be more closely aligned with Onithochiton. The inclusion of additional characters, such as tooth biomineralization, is strongly recommended in future studies of chiton taxonomy
