Anisonemia is a

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

single-celled A unicellular organism, also known as a single-celled organism, is an organism that consists of a single cell (biology), cell, unlike a multicellular organism that consists of multiple cells. Organisms fall into two general categories: prokaryotic ...

protist A protist ( ) or protoctist is any eukaryotic organism that is not an animal, land plant, or fungus. Protists do not form a natural group, or clade, but are a paraphyletic grouping of all descendants of the last eukaryotic common ancest ...

s belonging to the phylum

Euglenozoa Euglenozoa are a large group of flagellate Discoba. They include a variety of common free-living species, as well as a few important parasites, some of which infect humans. Euglenozoa are represented by four major groups, ''i.e.,'' Kinetoplastea, ...

, relatives of the

Euglenophyceae Euglenophyceae (ICNafp, proposed as a class) or Euglenea (ICZN, proposed as a class) is an unranked clade of single-celled algae belonging to the phylum Euglenozoa. They have chloroplasts originated from an event of secondary endosymbiosis with ...

algae Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthesis, photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular ...

. They are

flagellate A flagellate is a cell or organism with one or more whip-like appendages called flagella. The word ''flagellate'' also describes a particular construction (or level of organization) characteristic of many prokaryotes and eukaryotes and the ...

s, with two flagella for locomotion. Anisonemia includes various

phagotroph Phagocytosis () is the process by which a cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs phagocytosis i ...

ic species and a group of primary

osmotroph Osmotrophy is a form of heterotrophic nutrition and a cellular feeding mechanism involving the direct absorption of dissolved organic compounds by osmosis. Organisms that use osmotrophy are called osmotrophs. Osmotrophy is used by diverse groups ...

ic protists known as Aphagea.

Description

Members of Anisonemia are unicellular

s that have

flagella A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...

for movement. Species of this lineage have two flagella arising from the

anterior Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position pro ...

region of the cell, unlike their relatives,

Peranemida The peranemids are a group of phagotrophic flagellates, single-celled eukaryotes or protists. They belong to the Euglenida, a diverse lineage of flagellates that contains the closely related euglenophyte algae. Like these algae, peranemids ha ...

and

, where only one flagellum is emmergent. They move through a gliding motion, where the posterior flagellum is fully in contact with the substrate and the anterior flagellum beats through its whole length in front of the cell, carrying it forward.

Evolution

Anisonemia is a

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

group, or

, of

s that contains several

ic species and a clade that has evolved toward primary

osmotrophy Osmotrophy is a form of heterotrophic nutrition and a cellular feeding mechanism involving the direct absorption of dissolved organic compounds by osmosis. Organisms that use osmotrophy are called osmotrophs. Osmotrophy is used by diverse groups o ...

, named Aphagea. Anisonemia belongs to the Euglenida, a diverse group of flagellates that also contains the

phototroph Phototrophs () are organisms that carry out photon capture to produce complex organic compounds (e.g. carbohydrates) and acquire energy. They use the energy from light to carry out various cellular metabolic processes. It is a list of common m ...

. Together with other flagellates, they compose the phylum

. In particular, Anisonemia, Euglenophyceae and the phagotrophic Peranemida form a

known as

Spirocuta Spirocuta () is a clade of euglenids, single-celled eukaryotes or protists belonging to the phylum Euglenozoa. They are distinguished from other euglenids by active deformation of their cell shape, a process called euglenid motion or metaboly. Thi ...

, 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 Spirocuta () is a clade of euglenids, single-celled eukaryotes or protists belonging to the phylum Euglenozoa. They are distinguished from other euglenids by active deformation of their cell shape, a process called euglenid motion or metaboly. Thi ...

. The following cladogram depicts the evolutionary relationships of Anisonemia:

Classification

Anisonemia was first described by American protozoologist

Thomas Cavalier-Smith Thomas (Tom) Cavalier-Smith, FRS, FRSC, NERC Professorial Fellow (21 October 1942 – 19 March 2021), was a professor of evolutionary biology in the Department of Zoology, at the University of Oxford. His research has led to discov ...

in 2016, on the basis of

phylogenetic In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as phylogenetic inference. It infers the relationship among organisms based on empirical dat ...

analysis. He proposed it as a subclass of the obsolete class Peranemea, which is

paraphyletic Paraphyly is a taxonomic term describing a grouping that consists of the grouping's last common ancestor and some but not all of its descendant lineages. The grouping is said to be paraphyletic ''with respect to'' the excluded subgroups. In co ...

with respect to

, containing

in addition to Anisonemia. To date, it is the most diverse

heterotroph A heterotroph (; ) is an organism that cannot produce its own food, instead taking nutrition from other sources of organic carbon, mainly plant or animal matter. In the food chain, heterotrophs are primary, secondary and tertiary consumers, but ...

ic clade within

. It contains two orders, differentiated by their modes of locomotion: Anisonemida,

s 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, better known as Aphagea. Later revisions to the classification of

s ignored this taxon, until phylogenetic studies of the 2020s supported its

monophyly In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent comm ...

. In some studies, it is referred to as Anisonemea. The composition of Anisonemia is the following: * Order Anisonemida ** Family

Anisonemidae Anisonemidae is a small family of euglenid algae, with two accepted genera. It is the only family in the order Anisonemida. Description The family consists of single-celled organisms with a larger posterior flagellum by means of which they are ab ...

* Order Natomonadida ** Suborder Metanemina *** Family Neometanemidae ** Suborder Aphagea (=Rhabdomonadina ) *** Family Astasiidae *** Family Distigmidae

References

{{taxonbar, from=Q61996144 Taxa described in 2016 Taxa named by Thomas Cavalier-Smith Euglenozoa taxa