[1] Peranema cells are gliding flagellates found in freshwater lakes, ponds and ditches, and are often abundant at the bottom of stagnant pools rich in decaying organic material.

[3] However, while Peranema lack a localized photoreceptor, they do possess the light-sensitive protein rhodopsin, and respond to changes in light with a characteristic "curling behaviour.

[6] Peranema was correctly identified as a flagellate by Félix Dujardin, who created the genus in 1842, giving it the name Pyronema, for its pyriform (pear-shaped) body.

With this type of pellicle, which is shared by many euglenids, the spiraling microtubular strips are able to slide past one another, giving the organism an extremely plastic and changeable body shape.

At the tip of the flagellum, a short segment beats and flails in a rhythmic manner, possibly as a mechanism for detecting and contacting potential prey.

[14] Next to the reservoir, lies Peranema's highly developed feeding apparatus, a cytostomal sac supported on one side by a pair of rigid rods, fused together at the anterior end.

Some early researchers speculated that it might assist Peranema in tearing up and consuming its food; while others held that it was actually a tubular construction, serving as a cytopharynx.

[16] Brenda Nisbet questioned this, on the grounds that, when examined closely with an electron microscope, the rod-organ is blunt, and therefore an improbable instrument for either cutting or piercing.

Since the rod-organ had been seen to move back and forth during feeding, Nisbet argued that its primary function is to create suction, drawing prey into the cytostome.

[17] When Dujardin created the genus Peranema in 1841, he was unable to detect the second flagellum and classified it with other ostensibly uniflagellate "Eugléniens," Astasia and Euglena.