Zebrafish ALO variability, dermal microridges, and cortical epithelial cells. (A–C) Stereomicroscopic images of ALOs from different 10-mo-old EK wild-type zebrafish, with dashed white lines indicating the ALO border, showing a single ALO (A), double ALO (B), and an ALO with melanophores on it (C). (D–G) Movat’s pentachrome–stained transverse paraffin sections through the ALOs of two different adult zebrafish showing their morphological variability, including (D and E) a medulla divided into three compartments and (F and G) a fish with two separated ALOs. The blue boxes in panels D and F show the areas magnified in panels E and G, respectively. (H–J) Skin microridges on the outside of the ALO shown in a DIC micrograph (H) and in a rendering of an array tomography 3D image volume reconstruction (I and J), with a 3D reconstruction of the entire array in panel I and part of a single plane shown in panel J (see also Videos 2 and 3). (K) Single pseudocolored section from an array tomography image stack of an adult zebrafish ALO, highlighting the surface, mid-level, and basal epithelial layers. (L and M) Transmission electron micrograph of a microridge (orange arrows) containing surface epithelial cell. Panel M shows a higher magnification image of the orange boxed area in panel L, with a cell–cell tight junction (black arrow) and desmosome (yellow arrow) noted. (N–P) Transmission electron micrograph of a mid-level epithelial cell. Panels O and P show higher magnification images of the blue boxed areas in panel N, with desmosomes (yellow arrows in panel O) and intermediate filaments (panel P) noted. (Q–S) Transmission electron micrograph of a basal epithelial cell. Panels R and S show higher magnification images of the pink boxed areas in panel Q, with the basement membrane separating the dermal cortex and the medulla (red arrows in panel R) and a basal cell–basal cell desmosome (panel S) noted. See Video 2 for additional array tomography images of cortical epithelial cells. Scale bars = 150 µm (A–C, E, and G), 250 µm (D and F), 10 µm (H), 1 µm (J), 5 µm (K), 2 µm (L, N, and Q), 500 nm (M, O, P, R, and S), 200 nm.