Didinium

The Didinium belongs to the Phyllum Ciliophora. They are from 80-200 um long. Didinium are fast moving carnivorous protozoans that feed almost exclusively on live Paramecium. When its “nose” (shown at top) strikes a Paramecium it latches on with a threadlike trichocyst. Once captured and paralyzed, the didinium devours the Paramecium whole.
The “C”-shaped structure inside the body is a band shaped nucleus and can sometimes be seen with a regular light microscope.

Didinium will encyst when the food source is depleted and excyst when the food returns.