Didinium after ingesting Paramecium, coloured scanning electron micrograph (SEM). Didinium nasutum is a single-celled ciliate protozoan found in freshwater and marine habitats. It is a predatory organism, feeding on other ciliate protozoans, mainly Paramecium. Here, it has nearly completely ingested a Paramecium through its 'mouth' or cytostome. Didinium's two girdles of cilia are visible, used for locomotion. The proboscis of Didinium is beginning to reform. Also visible are bacteria (rod-shaped, green) on the surface of the protozoan.
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