English: "All specimens were preserved in petrographic thin sections from the Diabaig Formation stratotype, Lower Diabaig, Scotland, UK. Scale bars in (A)–(J), 5 μm; scale bar in (K), 10 μm.

(A) Bicellum brasieri n. g. n. sp. holotype specimen. Arrows indicate condensed, intracellular organic “spots” Sample TS09-1. (B) Bicellum brasieri n. g. n. sp. paratype. Larger ellipsoidal specimen with incomplete preservation in the interior. Circle indicates an example of a Y-shaped junction. Sample TS09-1. (C) Enlargement of holotype specimen showing typical “Y” junctions (circle) and a condensed intra-cellular “spot.” Total field of view is 10 μm. (D) Specimen in equatorial view in which the interior cells are only very faintly preserved. Sample TS09-2. (E) Surface view of specimen in (D), showing the tiled sets of parallel-aligned elongate cells. (F) Specimen in sub-equatorial optical section showing elongate exterior cells in surface view and the thinner walled isodiametric cells of the interior stereoblast. Sample TS09-2. (G) Surface view of specimen in (F), showing the tiled pattern of sets of elongate cells. (H) Scanning electron microscopy (SEM) image of an in situ milled medial section through B. brasieri. Sample TOR11-108. (I) SEM image of a milled tangential section of same specimen as in (H). Note that, here, the cells of the surface layer are quite elongate. (J) B. brasieri transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDS) elemental map of carbon revealing the thicker walled outer layer of sausage-shaped cells compared with the interior cells that have thin to partially absent membranes. Sample TOR11-108. (K) Larger, fragmented specimen of B. brasieri showing surficial cells in transverse and tangential sections. Note the elongate nature of the tangential cells and the lack of clearly delineated interior cells. Sample TS09-1, Diabaig Formation stratotype, Lower Diabaig, Scotland, UK.

See also Figures S1–S3 for additional examples and Table S1 for related cell size data."