The crossword solution for the term DIATOM is ALGA, which stands for 'ALGAE'. ALGAE are a large and diverse group of aquatic organisms that can range from single-celled microorganisms to multicellular forms. Diatoms are a type of ALGAE that are characterized by their cell walls made of silica. They are found in both freshwater and marine environments and are an important part of the food chain. Diatoms are also used in many industries, such as water filtration and food production.