Transmission electron micrographs of Symbiodinium psygmophilum cells. (A) Transverse section of a mastigote cell showing the pyrenoid (PY), nucleus, chloroplasts (c), type E eyespot (stigma), lipid globules (L), and starch (st). (B) Type E eyespot consisting of multiple layers of rectangular electron-translucent vesicles, or crystalline deposits (stigma, white arrow). (C) Cell with many chromosomes in the nucleus. (D) Single pyrenoid with two stalks (white arrowheads), located in the central part of each cell and surrounded by a distinct polysaccharide cap. Scale bars represent: A & C, 1 μm; B & D, 0.5 μm.