SEM of actively swarming P. vortex cultured on 1.5% (w/v) agar MH plates. A. Overview of small rotating colony which is contacting another moving and similar-sized colony (top) and extending a short process that is likely to be the start of a third mass (bottom). B. Center of colony with typical vortex pattern. C. Swarming P. vortex showing entangled flagella. D. Attachment to cells of filaments presumed to be flagella. Scale bar in (b) 5 μm, 1 μm when applied to (C) and 400 nm in (D).