Figure 2.

Ca. Ichthyocystis sp. and Ca. Similichlamydia sp. cysts in adjacent gilthead seabream gill filaments. (A) An overview, with the darkly stained Ca. Ichthyocystis sp. cysts (^*) typically attached to the base of the primary lamella, and filling the space between two secondary lamellae, which become surrounded by proliferating epithelial cells, completely embedding the cyst. The Ca. Similichlamydia sp. cysts (boxed or with arrows) are lightly stained, often in clusters, and typically localized within the base of the primary lamella. (B1–B4) Serial 1 μm sections (although not sequential) of two small cysts with host cell nucleus (arrows) pressed between the inclusion and the cellular membrane. Regions shown were enlarged from region of small rectangular box, upper right of overview (A). (C) Higher magnification of boxed region, lower right (A), for better visualization of similichlamydial cysts, all with broad inclusion membranes. Semi-thin 1 μm sections were stained with toluidine blue and imaged using a Hamamatsu Nanozoomer slide scanner, equipped with a 25 x NA 0.75 objective lens, producing images with pixel sizes of 0.25 μm. Scale bars are 100 μm in (A), 10 μm in (B1–B4), and 25 μm in (C).