Falcidens is one of three genera within the family Chaetodermatida; its radula consists of a single row of teeth which are mineralized in crystalline hydroxyapatite (a most unusual mineral in organisms), and its teeth are not periodically shed and replaced like in other molluscs.
For details of the radula, see Radula#In caudofoveates.
↑Metscher B. D. (2009) "MicroCT for comparative morphology: simple staining methods allow high-contrast 3D imaging of diverse non-mineralized animal tissues". BMC Physiology 9:11. doi:10.1186/1472-6793-9-11 Cropped from figure 13.