A1. NONMOTILE ALGAE WITHOUT CHLOROPLASTS: CYANOBACTERIA
A2. NONMOTILE ALGAE WITH CHLOROPLASTS
B1. CELLS USUALLY SOLITARY
B2. NONMOTILE COLONIES WITH TWO OR MORE CELLS
B3. FILAMENTOUS ALGAE (INCLUDING PSEUDOFILAMENTS)
B4. CELLS ATTACHED TO ZOOPLANKTON (EPIZOIC), LIVING INSIDE ZOOPLANKTON OR OTHER AQUATIC ANIMALS (ENDOZOIC), OR ATTACHED TO AQUATIC PLANTS (EPIPHYTIC)
A3. MOTILE ALGAE WITH CHLOROPLASTS AND FLAGELLA
A4. CELLS DIVIDED INTO MIRROR-IMAGE SEMI-CELLS: Desmids (see key at cedar.wwu.edu/cedarbooks/14/ )
A5. CELLS ENCLOSED IN GLASSY, ORNAMENTAL FRUSTULES: Diatoms (see key at diatoms.org)