"Tetraselmis" species vary greatly in cell size and shape. Cells can be round, ovoid, elliptical, flattened, compressed, or a combination of these shapes, in which their side lengths can vary in range from 3.5-25 µm. "Tetraselmis" cells have four flagella of equal length, which emerge from a depression near the apex. In most species, the flagella emerge in pairs and project away from each other. Generally, individual cells travel in a linear fashion for a long period of time, and then rapidly change direction without stopping, in which their flagella generate force for motion through an aqueous environment. See figure 1 for general features of the flagella and cell body of "Tetraselmis" species.