Gonyostomum semen is a colonial freshwater organism characterized by cylindrical cells arranged in chains. Each cell is elongated with two flagella, one long and one short, located at the anterior end. Chloroplasts are present, typically disc-shaped and distributed peripherally within the cells. Reproduction occurs through both asexual cell division and sexual formation of resting spores. Commonly found in lakes and ponds, Gonyostomum semen can form blooms under favorable environmental conditions, making it significant in freshwater ecosystems.