Hemimastigophora is a group of single-celled eukaryotic organisms including the Spironematellidae, first identified in 1988,[1][2][3] and the Paramastigidae.

[1] Its placement on the eukaryote tree of life was unclear, but the authors suggested that the structure of its pellicle and cell nucleus indicated a close relationship with Euglenozoa.

During that time, researchers proposed that it should be classified in, or near, an assortment of other groups, including the alveolates, apusomonads, ancyromonads, and Rhizaria.

[3][4] In an article published in 2018, Lax et al. announced that a new hemimastigophoran species, Hemimastix kukwesjijk, had been discovered in a Nova Scotian soil sample, and successfully cultivated in the laboratory.

Phylogenomic analyses of the two organisms suggest that Hemimastigophora is a very ancient lineage, which diverged from the other eukaryotes at such an early date that the group should be classified at the supra-kingdom level.