Hairybacks (Gastrotricha) (Figs. 45/1–2) are microscopic organisms up to 600 µm. These bilateral animals have elongated, wormlike body. Their body surface is covered with cilia arranged in longitudinal and transverse stripes. Despite their common name cilia are more frequent on the ventral surface than on the back. With these organelles the flexible animals move quickly on the mud surface rich in decaying debris or amongst water plants where they feed on algal cells and bacteria.