Changes in the morphology of the radula in the giant key-hole limpet (GKL) were analyzed including radula length, width, number of rows, and the morphology of the teeth in each row through ontogeny. In postlarvae with a shell length (SL) of 700 mm, the radula is ∼240 mm long and composed of about 30 rows of teeth. Each row has a central rachidian tooth, which has a pointed tip similar to the three pairs of lateral teeth on either side. These are flanked by five pairs of marginal teeth. In GKL with an SL of ∼2 mm, the teeth are larger, the rachidian tooth no longer has a triangular tip and lies flat along the radular ribbon except for a curled cusp. The most distal lateral tooth is larger than the other lateral teeth and has a sharply pointed tip, and the number of marginal pairs has increased from 18 to 20. InGKLwith an SL of 6–8 mm, the radula is∼2mmlong. The large, flat rachidian tooth overlaps and covers the laterals except the fifth lateral, which is now much larger and tapers to a sharp point. By the time GKL have an SL of 11 mm, the radula is about 3 mm long and tooth morphology is the same as in larger animals except for a gradual increase in tooth size and differentiation of the marginal tooth tips into three varieties. Scanning electron microscopy with energy-dispersive X-ray spectroscopy demonstrates that the radula is not mineralized and signs of wear and breakage are common on teeth in the first five to seven rows, the rows that are actually extended out of the mouth during a feeding motion.