Anisonemia

Anisonemia is a monophyletic group, or clade, of flagellates that contains several phagotrophic species and a clade that has evolved toward primary osmotrophy, named Aphagea. Anisonemia belongs to the Euglenida, a diverse group of flagellates that also contains the phototrophic Euglenophyceae.^[2] Together with other flagellates, they compose the phylum Euglenozoa.^[1] In particular, Anisonemia, Euglenophyceae and the phagotrophic Peranemida form a clade known as Spirocuta, distinguished by a greater number of pellicle strips than other euglenids. These strips allow the cells to actively deform their shape, a unique characteristic known as metaboly.^[2] The following cladogram depicts the evolutionary relationships of Anisonemia:^[2][3]

Anisonemia was first described by American protozoologist Thomas Cavalier-Smith in 2016, on the basis of phylogenetic analysis. He proposed it as a subclass of the obsolete class Peranemea, which is paraphyletic with respect to Euglenophyceae, containing Peranemida in addition to Anisonemia. To date, it is the most diverse heterotrophic clade within Spirocuta. It contains two orders, differentiated by their modes of locomotion: Anisonemida, phagotrophs that perform a gliding motion with their anterior flagellum, and Natomonadida, which move by swimming. In turn, Natomonadida comprises two suborders: the phagotrophic Metanemina and the completely osmotrophic Rhabdomonadina.^[1] Later revisions to the classification of protists ignored this taxon,^[4] until phylogenetic studies of the 2020s supported its monophyly. In some studies, it is referred to as Anisonemea.^[3] The composition of Anisonemia is the following:

• Order Anisonemida Cavalier-Smith, 2016
  • Family Anisonemidae Kent, 1880 emend. Cavalier-Smith, 2016
• Order Natomonadida Cavalier-Smith, 2016
  • Suborder Metanemina Cavalier-Smith, 2016
    • Family Neometanemidae Cavalier-Smith, 2016
  • Suborder Rhabdomonadina Leedale, 1967 emend. Cavalier-Smith, 1993
    • Family Astasiidae Kent, 1884
    • Family Distigmidae Hollande, 1942