Transmission electron micrographs (TEM) showing the general morphology of Calkinsia aureus. A. Sagittal TEM showing the nucleus (N) with condensed chromatin and a conspicuous nucleolus (Nu), a battery of extrusomes (E), the vestibulum (V) located on the dorsal side of the cell, ingested material and epibiotic bacteria on the extracellular matrix. The extrusomal pocket (EP) branched from the vestibulum (V) (bar = 4 μm). B. Ingested material containing diatom frustules (arrow). (bar = 2 μm). C. Cross section of the cell through the nucleus (N), the battery of extrusomes (E), the flagellar pocket (FLP) and the feeding pocket (FdP). (bar = 2 μm). D. High magnification view through the vestibulum (V) that is opened on the ventral side of the cell. E. High magnification view through the anterior opening showing the termination of the extracellular matrix (double arrowhead) and fine somatonemes (S) or hair-like structures on the perforated matrix (arrows) that is not covered with epibiotic bacteria. The arrowhead indicates the supportive microtubular sheet that lines the inside of the cytostome and turns along the cell surface. (D, E, bars = 1 μm). F. Hairs (arrow) on the wall of the vestibulum (V). (bar = 1 μm). G. Cross section showing the battery of tubular extrusomes (E). (bar = 2 μm).