Ultrastructure of Pleromin, a Highly Mineralized Tissue Comprizing Crystalline Calcium Phosphate Known as Whitlockite, in Holocephalian Tooth Plates

Abstract

The gross structure and microstructure of holocephalian tooth plates were initially investigated by Bargmann (1,2) and Brettnacher (3). Ørvig (4,5,6) subsequently reported in the detail microstructural characteristics of both extant and fossil holocephalian tooth plates. These studies indicate the holocephalian tooth plate to consist of bony tissue and hypermineralized pleromin (4), with the hardness of pleromin comparable to that of enamel and enameloid. Ishiyama et al. (7) found the crystalline material of pleromin to be not hydroxyapatite but whitlockite by a powder X-ray diffractometry, and pleromin to be the sole sound dental tissue consisting of whitlockite in vertebrates.