Oocystis submarina, a green algae species, is characterized by its small, spherical or nearly spherical cells that often aggregate into colonies. Each cell has a smooth and delicate cell wall without distinct ornamentation, housing one or more disc-shaped chloroplasts containing pyrenoids for photosynthesis. The nucleus is centrally positioned within the cell. Colonies are formed through cells held together by a mucilaginous matrix. Reproduction occurs either through cell division within colonies or the production of zoospores under specific environmental conditions. Oocystis submarina thrives in freshwater habitats such as lakes, ponds, and slow-moving streams, demonstrating adaptations suited for these aquatic environments.