The largest single-cell organism is the giant amoeba known as Gromia sphaerica. This fascinating organism can reach sizes up to several centimeters in diameter, making it visible to the naked eye. Gromia sphaerica is typically found in marine environments, where it moves and feeds by extending its surrounding cytoplasm into pseudopodia. Despite being a single-celled organism, it exhibits incredible complexity and displays unique behaviors, showcasing the diversity of life forms on Earth and the adaptability of organisms in various ecological niches.