Composite image of Didinium nasutum attacking and ingesting a Paramecium. Didinium nasutum is a one-celled, barrel-shaped ciliate characterized by two bands of cilia around its body. It is commonly found in bodies of fresh or brackish water, where it is a voracious predator of its main food source, the much larger unicellular ciliate Paramecium. Didinium attacks with poisonous trichocysts and attachment lines, and the Paramecium ejects its own trichocysts in defense. Didinium then engulfs its prey and digests it within a few hours, ready to hunt again. Composite of scanning electron micrographs (SEM), average magnification 1500x at 8"x10".