Fig. 2

Pinacoderm epithelia. A,B. Exopinacocytes in the exopinacoderm, viewed by SEM (A), and by fluorescence using the membrane marker FM 1-43 (B). C Cross section of the ‘tent’ viewed from the underside showing elongate endopinacocytes that have pulled away from one-another during fixation. D View of the collagen layer under the exopinacocytes and being secreted by a lophocyte. E Cross section of a junction between two exopinacocytes fixed with ruthenium red, illustrating that the stain does not penetrate the junction, and that the exopinacocytes are underlain by collagen. F,G Cross section of the ‘tent’ showing exopinacocytes underlain by a thin layer of collagen. Mesohyl cells lie between the exo and endopinacoderms. A,C,D,F: SEM; B: Fluorescence; E: Transmission electron microscopy (TEM). exp, exopinacocytes; end, endopinacocytes; col, collagen; RR, ruthenium red; me, mesohyl