Silica Biomineralization in the Radula of a Limpet Notoacmea schrenckii (Gastropoda: Acmaeidae)

379 Biominerals are the inorganic phases of minerals found in biological systems, which are distributed from microorganisms to the highest animals and plants (Mann et al. 1989, Simkiss and Wilbur 1989, Weiner and Lowenstam 1989, Mann 2001). Although minerals composed of calcium predominate, biominerals of barium, strontium, iron, and silica are also well known. Biominerals generally occur as oxides, hydroxides, phosphates, and carbonates (Webb et al. 2001). Biosilicification, the biological formation of opal-like amorphous hydrated silica, occurs in a wide variety of organisms, including diatoms, sponges, mollusks, and higher plants (Voronkov et al. 1977, Lowenstam 1981, Simpson and Volcani 1981). Among various organisms with the capability to deposit silica, diatoms and sponges are the most thoroughly explored taxa. In the study of diatoms, species-specific polypeptides were identified to co-precipitate with amorphous silica during the cell wall-formation process (Kröger et al. 1997 1999). These polypeptides are so tightly associated with the amorphous silica that they can only be extracted after dissolution of the cell wall in hydrogen fluoride (HF) to remove the silica. The HFextractable polypeptides were named silaffins and were demonstrated to act as regulating molecules during biosilica formation in diatoms (Kröger et al. 1999 200