The reference to “algae” in the name of these organisms indicates that the designation is used loosely for they are often considered to be more closely related to bacteria than to true algae.
The cell walls of blue-green algae differ from those of most bacteria in that they usually contain cellulose, but like those of bacteria, they also usually seem to contain muramic acid. Outside the cell wall proper, there is often a layer of a more or less firm, gelatinous material called a sheath, composed of pectic materials.