(pro-tass-piss) is a medium-sized heterotrophic flagellate. Two flagella emerge close to each other from a point behind the apex of the cell and on the ventral side. The anterior flagellum is typically shorter than the posterior flagellum. The ventral side may give rise to pseudopodia which can enclose food - such as diatoms. In this image, many cells have fused into a syncitium. DIfferential interference microscopy.