In this section
Unbranched cyanobacterial filaments of blue-green cylindrical cells in a thin sheath. Cells are often at least as long as they are wide. Cells at the end of the filament are not tapered/pointed, and lack a calyptra (thickened cap; cf. Phormidium). Filaments break easily. Heterocytes absent. Organelles are absent from the cells, but granules are common.