Subsequently, fusion of gametes completes the cycle. Classification of Protista Autotrophic protists are called algae. In algae, the body is called a thallus since it lacks roots, stems and leaves. Differences between groups are due to diversity in photosynthetic pigments, carbohydrate food reserves, number and position of flagella, life cycle patterns and cell wall characteristics. One group contains diatoms , which create silicate shells found in diatomaceous earth.
Green algae are diverse, and are presumed to be the ancestors of green plants.
Brown algae, include forms which are very important both ecologically and economically. Extracts are used in food products, cosmetics, animal feeds, fertilizer, et al. Protozoans are heterotrophic protists. This assemblage includes a variety of taxa. Fungus-like protists include slime molds and water molds.