Fig. 5. Double immunofluorescence localization of H⁺-ATPase (green; A,A') and Na⁺/K⁺-ATPase (red; B,B') in the gills of a freshwater ammocoete of P. marinus with the corresponding merged image overlaid with DAPI nuclear staining (blue) and differential interference contrast (DIC) for orientation (C,C'). The area within the box has been enlarged 3x. Arrows indicate apical H⁺-ATPase labelling and arrowheads indicate basolateral Na⁺/K⁺-ATPase labelling. Scale bar, 50 µm.