Phacus acuminatus is a freshwater unicellular organism characterized by its elongated, spindle-shaped cell. It has a firm pellicle with longitudinal or spiral striae and two flagella of unequal length: a longer posterior flagellum and a shorter anterior flagellum with a stigma for light perception. The cell contains numerous discoid or band-shaped chloroplasts responsible for photosynthesis and paramylon bodies for storing reserve carbohydrates. Reproduction occurs primarily through asexual longitudinal fission. This species is commonly found in ponds, lakes, and slow-moving rivers, playing a role in freshwater ecosystems.