Cells have constrictions between them (filamentous desmids).
Cell walls composed of overlapping pieces that are H-shaped in optical section (often visible at break points); pyrenoids are absent.
Cell wall is smooth and featureless; filaments are long and cells are not easily dissociated.
Some cell walls have cell division scars visible at one end; pyrenoids present in chloroplasts.
Cell wall is smooth and featureless; filaments are short and easily dissociated; chloroplasts one to a few per cell, small and discoid.