During evolution silica deposition has been used in Protozoa, Metazoa and in plants as skeletal elements. It appears that the mechanisms for the formation of biogenic silica have evolved independently in these three taxa. In Protozoa and plants biosilicification appears to be primarily driven by non-enzymatic processes and procedes on organic matrices. In contrast, in sponges (phylum Porifera) this process is mediated by enzymes; the initiation of this process is likewise dependent on organic matrices. In this monograph the role of biosilica as stabilizing structures in different organisms is...