In this section
Unbranched filaments of short cylindrical cells in a fine sheath. Filament may glide within the sheath. Cells may be at least as long as they are wide (cf. Oscillatoria). End cells often pointed/tapered, with a calyptra (thickened cap) on the terminal cell. Tapering may extend several cells from the end. Heterocytes absent. Organelles absent from the cells, but granules/vesicles common. Forms mats that may be dark brown, green, purple or blue-green.