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Unbranched cyanobacterial filaments of small cylindrical blue-green cells. Filaments appear to have slight gaps between cells in addition to the constrictions at cross walls, due to the presence of aerotopes (agglomerations of gas vesicles) at the cell poles. Blue-green colour inside the cells is often denser at the edges, due to peripheral location of thylakoid membranes. Organelles absent from cells.