Abstract
The major lateral teeth of the chiton radula are heavily mineralized with iron and calcium biominerals, with the delivery of ions thought to be effected by the overlying superior epithelial tissue, which surrounds the tooth cusps at all stages of development. Centrally located within the bases of the mineralized teeth is a cell filled cavity, referred to as the stylus canal. The cells within the canal are continuous with the superior epithelial tissue and appear to terminate at the junction of the tooth base and cusp. This junction zone has previously been reported to be the initial site of ion deposition in chiton teeth. As such, the cells within the stylus canal are in an ideal location for the delivery of ions to this region. However, past histological examinations have focused on the cells abutting the cusp surface, while the cells of the canal have been virtually ignored. In order to elucidate the structure and function of the cells within the stylus canal a histological investigation has been undertaken, using light microscopy, and transmission and scanning electron microscopy. In addition, the radula teeth have been analyzed using Xray microanalysis (EDS). The mechanisms of ion delivery to the mineralization fronts within the tooth cusps is currently poorly understood, and the reasons for the initial deposition of ions into the junction zone has been confounding, both in regard to how the ions get there and why they are deposited there first. Proof of the existence of a subsidiary ion delivery mechanism has the potential to significantly enhance our understanding of the iomineralization pathways in these animals. The overall morphology of the stylus canal and ultrastructure of the canal cells will be presented and the role of the cells as a significant pathway for the delivery of ions to the developing major lateral teeth will be discussed.