Anisonema Dujardin 1841

Sphenomonadine euglenid, almost rigid, gliding cells with two emergent flagella, recurrent flagellum well developed (thick) basally, forming a hook, gliding interrupted by sudden jerks, mouth not visible by light-microscopy, although ultrastructural studies suggest that it is present, marine and freshwater, benthic, type species A. acinus.

The members of Anisonema have two, heterodynamic flagella; unequal in length; both emergent from the canal; the shorter, thinner flagellum beats actively with a sweeping motion, is directed anteriorly and the longer one trails posteriorly and is up to three times the length of cell. The trailing flagellum forms a hook as it leaves the flagellar pocket and bends backward. This feature is not unique to the genus Anisonema and may be encountered in the genus Dinema and Ploeotia. Cells of Anisonema are slightly dorso-ventrally flattened with limited metabolic capacity and no visible mouth. Pellicle smooth or with fine ridges. Anisonema has a distinctive movement in which gliding is interrupted by sudden backward jerks. The genus Anisonema contains about 25 species. The most commonly reported species from freshwater and marine sites is Anisonema acinus.

Anisonema is a genus of colorless flagellates that occur in marine, brackish, and freshwater habitats. The cell is typically ovoid, somewhat flattened, and rigid. The name Anisonema derives from Greek for "unequal thread", in reference to the two flagella that are of unequal lengths. The shorter flagellum extends forwards and propels movement with a sweeping motion, while the longer flagellum, up to three times the length of the cell, trails behind, with jerking contractions.

The genus was first named by French biologist Félix Dujardin his 1841 Histoire naturelle des zoophytes. Infusoires, comprenant la physiologie et la classification de ces animaux, et la manière de les étudier à l'aide du microscope.

As of 2020, there are around 20 accepted species in the genus.

This authority places the genus under the family Sphenomonadidae