Calcification, Silicification, Bioerosion
Members of the phylum Porifera constitute an amazing array of species in terms of the kinds and shapes of mineral products they secrete. Depending upon the group, relatively enormous amounts of aragonite, calcite, and silica are secreted by these animals. In viewing sponges from this perspective, one is impressed by the diversity of transport and secretory mechanisms that have evolved in the phylum coupled with the almost total absence of the evolution of discrete tissues involved in these phenomena. In view of the fact that sponges lack an intraorganismal transport system, their capacity to secrete these minerals in large quantities is all the more amazing. The processing of precursors must be highly efficient on a cell to cell basis and may also functionally involve the intercellular matrix, although data on the latter point are not yet available. In a small number of species, the animals are capable of eroding calcareous substrata through a process assumed also to involve transport and secretory processes; these result both in the partial dissolution and the subsequent removal of the substratum.
KeywordsSilicic Acid Sponge Tissue Axial Filament Calcareous Substratum Calcareous Sponge
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