Algae microscopic refers to two types of microscopic algae, diatoms and desmids. Diatoms are single-celled algae with a silica shell that are found in both fresh and salt water. Desmids are single-celled green algae that live in freshwater and are characterized by their symmetrical shape. Both diatoms and desmids are important components of aquatic ecosystems, providing food for other organisms and helping to cycle nutrients.