Cells are 15 to 19 microns long, very slender and spindle-shaped. Two flagella insert at a wide angle at the base of a short rostrum. The anterior flagellum is one to two times the length of the body, is thicker than the posterior flagellum and inserts in a small flagellar pocket. The posterior flagellum adheres to the body but extends behind the cell by about half a body length and tapers posteriorly. A small contractile vacuole is located at the base of the rostrum. The nucleus is centrally located. Refractile granules are present throughout the cell. When swimming, cells are stiff and rotate rapidly and the anterior flagellum beats rapidly and strongly. Non-swimming cells may glide, partly on the posterior flagellum and may be very plastic. During gliding, the anterior flagellum beats with an undulating pattern and the adhering portion of the posterior flagellum follows a gently spiralling path. Gliding cells change direction frequently by bending back on themselves.