Peranema are small flagellates and range in size from 20-70µm in diameter. They are very active predators and scavengers.

This flagellate is common in waters rich in organic nutrients, especially in water in which decay is taking place.

The single flagellum projects straight forward, and a rapid rotation of its extreme end pulls the Peranema smoothly through the water. The body of the Peranema can undergo extreme contraction and distortion as it moves.

Peranema have been seen inside the bodies of dead rotifers and are said to absorb nutrients through their outer pellicle. In addition, they can ingest quantities of detritus, bacteria, algae and even large organisms by expansion of the cytostome -- a cavity which lies at the base of the flagellum.