N reference 356), and ion carriers (Fig. 6). Coral calcification is an extracellular process (177) that occurs within the ECM. It has been suggested that this medium is a colloidal gel matrix secreted by the calicoblastic cells (52, 71, 177); however, the physicochemical characteristics of this medium are still a matter of debate (for reviews, see references 6 and 357). Nevertheless, it must be al