Possession of flagellum is not a taxonomic feature. many different unrelated organisms have flagellum. euglena, zooflagellates but also some fungi or even human sperm cells.
When tiny ice crystals in clouds stick together to form snowflakes, the result is snow. If enough crystals form a clump, they'll become heavy enough to fall to the ground. When temperatures are cold and moisture in the form of tiny ice crystals exists in the atmosphere, snow forms.
