Fig. 5. STEM image of a 1 µm-thick, freeze-substituted section of Galaxea fascicularis showing part of the extrathecal coelenteron (c), aboral gastrodermis (AG) and calicoblastic ectoderm (CE). Elemental images of Na, Cl, P, K and Ca are shown with the concentration (in mmol kg^–1) of each element represented by a grey scale. The Ca image shows the presence of loci of nucleating calcium carbonate deposits on the organic matrix.