Colorized scanning electron micrographs (SEMs) of a 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. This free living carnivorous protist is commonly found in bodies of fresh or brackish water.  It is a voracious predator of its main food source…the much larger unicellular, Paramecium.

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The Didinium attacks using specialized structures called toxicysts to ensnare and paralyze its ciliate prey. The Paramecium ejects its own trichocysts in defense, but to no avail. Once captured, the prey is engulfed through the Didinium’s expandible cytostome. Within a few hours, it is ready to hunt again. In the absence of food, a Didinium will encyst, lying dormant within a protective coating.

All images © Biophoto Associates / Science Source