(A) Cryo-ET image of a mitochondrion associated with FHV spherules, taken from a reconstructed tomogram obtained at 41,000 x magnification, defocus of −6. Mitochondrial outer membrane, spherule membrane, interior spherule filaments, and spherule aperture structures are indicated with red, blue, black, and white arrowheads, respectively, consistent with arrowhead colors used in Figures 5 and 6. Scale bar is 100 nm. (B–D) Segmentation of the white-outlined area in panel A. The Amira program (FEI) was used to trace and structurally segment spherule membrane in white and interior spherule density in red. Panels B and C provide three dimensional renditions, panel D segments the structure in a single plane. Scale bars are 50 nm. See Video 2 for complete tilt series.