A2. NONMOTILE ALGAE WITH CHLOROPLASTS

B1. CELLS USUALLY SOLITARY

C3. CELLS CLUB-SHAPED, CRESCENT-SHAPED, ELLIPTICAL, OR FUSIFORM IN OUTLINE

D3. CELLS BROADLY OR NARROWLY FUSIFORM IN OUTLINE

E1. CELLS BROADLY FUSIFORM OR CYLINDRICAL; RIBBON-LIKE SPIRALLING CHLOROPLAST(S) OR DENSE CHLOROPLAST WITH REDDISH END CAPS: Spirotaenia and Tortitaenia

E2. CELLS CLUB-SHAPED OR BROADLY FUSIFORM WITH MANY LONG APICAL BRISTLES AND A SHORT, SPLIT (BIFURCATE) POSTERIOR SPINE: Paradoxia

E3. CELLS NARROWLY OR BROADLY FUSIFORM WITH LONG APICAL SPINE AND POSTERIOR SPINES; POSTERIOR SPINES MAY BE SPLIT (BIFURCATE) OR END IN LEAF-LIKE STRUCTURE Ankyra and Lanceola

E4. CELLS BROADLY OR NARROWLY FUSIFORM; SOLITARY OR IN LENS-SHAPED COLONIES WITH CELLS OFFSET AND ALIGNED ALONG LONG AXIS; CELLS AND COLONIES ENCLOSED IN LENS-SHAPED MUCILAGE: Elakatothrix and Fusola

E5. CELLS FUSIFORM OR CYLINDRICAL; SOLITARY OR IN IRREGULARLY SPHERICAL COLONIES; CELLS ALIGNED ALONG LONG AXIS FORMING BUNDLES; COLONIES SURROUNDED BY DIFFUSE MUCILAGE: Quadrigula

E6. CELLS NARROWLY FUSIFORM; SOLITARY; LACKING ANY VISIBLE MUCILAGE LAYER; MAY FORM BLOOMS: Koliella, Monoraphidium, Schroederia, and similar