Major primary stages of biomineralization in radular teeth of the limpet Lottia gigantea

The radula (feeding organ) of the limpet Lottia gigantea is a membraneous ribbon to which are attached up to 150 transverse rows of teeth. The organic matrix of the teeth is impregnated with inorganic salts (Fe, Si, Ca). In its posterior end, the radula originates from a radular gland which is coiled dorsally, where long odontoblast cells secrete the tooth and the radular membrane. Teeth mature gradually. The organic matrix of this complex was stained homogeneously in the first five rows (hematoxylin-eosin). From Row 6 onward, the tooth became demarcated from the radular membrane by forming "segments" within the matrix of the radular membrane. The cusp's organic matrix milieu was histologically divided into two main domains, internal and external, each one consisting of fibrillar milieu. Teeth are embedded within the tall columnar superior epithelium, which superimposes the cusps. Iron-bearing granules started to appear in these cells beginning at Rows 7 to 10, increasing in number to Row 20 and continuing to at least Row 65. Iron proceeded to infiltrate first into the internal part of the cusp at Row 15. The outer part of the cusp was mineralized beginning at Rows 22 to 27. At about Row 30, the cusp was heavily mineralized by iron. Calcium was deposited into the radular membrane and tooth bases from the most posterior part. It is concluded that radula biomineralization is subject to highly complex but precisely controlled cytological-biochemical processes and that different parts of each young tooth are subjected simultaneously to different biomineralization pathways. Specimens used in this study were collected in 1984 from the intertidal zone at La Jolla, California.