Fig. 4.

Schematics of plausible mechanisms of iron sulfide mineralization in the scaly-foot snail. Scale-secreting epithelial cells produce sulfur-enriched channel-like columns (1) in which sulfur species are spontaneously diffused outward to the scale (2). Iron ions diffuse from the surrounding seawater and react with the sulfur species within the column to mineralize iron sulfides (3) and further grows depending on the iron concentration (i.e., distance from the surface) (4). Minerals generated in the surrounding environment are also deposited on the scales to form the outermost layer (5).