Figure 4
Backscatter electron microscopy images and stills from time-lapse movies comparing A. millepora' 's regular SBW with the enlarged tissues during the contact response phase. (a) A standard surface body wall (SBW) of A. millepora showing the two epithelial layers (epidermis; Ep, gastrodermis; Ga) separated by the mesoglea (Mes) and the cells and processes that characterise these layers; supporting cells (Sup), intercellular vacuole (Va) or spaces in between each cell, nematocysts (Nm), type 2 gland cell (Mu), Symbiodiniaceae (Sym) and the soluble surface mucus layer (SML). (b) Higher magnification image of the vesicles (white) in standard type 2 gland cells (mucocytes). (c, d) The soft tissue became enlarged at the points of contact between the coral and the substrate. (d) Electron microscopy images of the enlarged SBW tissues showed a proliferation of densely packed thin supporting cells and Symbiodiniaceae. and the differentiation/proliferation of type 4 (yellow) and type 1 and 2 (blue) gland cells (Sec) with lead to the loss of intercellular vacuoles. (e, f) Electron image showing the vesicles (Sec4) of type 4 gland cells with matter trapped inside and mucocytes (Sec2). (g) Closer look at the densely packed epitheliomuscular supporting cells (Sup) and their nuclei. Skeleton; Sk, surface body wall; SBW, epidermis; Ep, gastrodermis; Ga, mesoglea; Mes, surface mucus layer; SML, Nm; nematocyst, supporting cells; Sup, intercellular vacuole; Va, secretory cells; Sec, type 2 gland cell; Mu and Sec2, type 4 gland cell; Sec4, Symbiodiniaceae; Sym.
