Fig. 11. High-resolution NanoSIMS image of a 2 µm-thick, freeze-substituted section of Galaxea fascicularis after 8 min incubation in ⁴⁴Ca artificial seawater in the light. The ⁴⁰Ca image (A) shows very high levels of ⁴⁰Ca in cnidocytes and mucocytes in the oral ectoderm (OE) and oral gastrodermis (OG) compared with unspecialised ectodermal cells (E) and mesogloea (M). ETC, extrathecal coelenteron. The ⁴⁴Ca/⁴⁰Ca ratio image (B) indicates that ⁴⁴Ca had reached a high relative concentration in the unspecialised oral ectodermal cells (E) and mesogloea but relatively little exchange had occurred in the mucocytes (Mu) or cnidocytes (Cn).