English: Transmission electron microscopy (TEM) of Pandoravirus massiliensis. (A) Negative staining of a P. massiliensis particle: the ostiole (arrow) is located at the apex of the particle. Peripheral thin fibers can be observed enwrapping the particle (thin arrow in boxed zoomed region). (B) Ultrathin section showing (i) the most-peripheral sugars depicted by ruthenium red aggregates (thick white arrow and level 1 in boxed zoomed region); (ii) a thin electron-dense membrane (thick black arrow and level 3 in boxed zoomed region) and more centrally (iii) a thick bundle of tubules (thin white arrowhead and level 5 in boxed zoomed region). (C) Two thick tubules compose the inner-most thick layer (arrowheads). (D) Two particles with ostioles cut transversally or perpendicularly (white and black arrows). (E) The inner-most thick tubules with thick protrusions (white arrow in boxed zoomed region) toward the outer thin electron-dense membrane. (F) Thin fibers (white arrows in F1 and F2 boxed zoomed regions) projecting from the inner-most thick tubules, crossing the outer electron-dense membrane and reaching the peripheral ruthenium-red stained sugars.