Fig. 5. Representative electron micrograph of a seawater-acclimated opercular epithelium pretreated with cytochalasin D, then treated with a hypotonic shock to the basolateral side. Note the failure of the apical crypts to close over and the high crypt density similar to that of seawater controls (Fig.1). This micrograph also shows characteristic angular gaps between the cells (arrows). Scale bar, 10µm.