Fig. 7
Model of cortex development. a SEM image showing basic morphological features of cortex, b enlargement of fine irregular polycrystalline structure from the outermost cortex, c enlargement of the layered microspine from the inner cortex. d-i successive phases of cortex formation: microspine development (d), thickening of microspines (e), deposition of more massive stereom with conchoidal fracture on layered microspines between stromatic channels (f), development of spinules (g) formation of protuberances from spinules (h), eventual fusion of neighboring protuberances (i). Abbreviations: Spin - spinule, Pro - proturberances, Epi - epibionts, S - stereom, Ic - inner cortex, Oc - outer cortex, Ms - microspines, Firc - fine irregular crystal structure, Sc - stromatic channels, M - medulla, Rs - rectilinear stereom