Breviatea | |
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Breviata anathema | |
Scientific classification | |
Domain: | Eukaryota |
Clade: | Amorphea |
Clade: | Obazoa |
Class: | Breviatea Cavalier-Smith, 2004 [1] |
Order: | Breviatida Cavalier-Smith, 2004 [1] |
Family: | Breviatidae Cavalier-Smith, 2013 [2] |
Genera | |
Diversity | |
4 species |
Breviatea, commonly known as breviate amoebae, [3] are a group of free-living, amitochondriate protists with uncertain phylogenetic position. [4] They are biflagellate, and can live in anaerobic (oxygen-free) environments. [4] [3] [5] They are currently placed in the Obazoa clade. [6] They likely do not possess vinculin proteins. [6] Their metabolism relies on fermentative production of ATP as an adaptation to their low-oxygen environment. [4]
The lineage emerged roughly one billion years ago, at a time when the oxygen content of the Earth's oceans was low, and they thus developed anaerobic lifestyles. Together with Apusomonads, they are the closest relatives of the Opisthokonts, a group that includes animals and fungi. [3] [7]
Mitochondrion-related organelles (MROs) are organelles that evolved from a degradation of ancestral, fully functional mitochondria. Among Breviatea, MROs are present in Pygsuia , Breviata and Subulatomonas . In the cells of Pygsuia, for which the complete transcriptome is known, there is a single smooth MRO that lacks a mitochondrial genome and most components of the electron transport chain. Of the citric acid cycle enzymes, which are present in the mitochondria in other organisms, only two are present in Pygsuia: fumarase and succinate dehydrogenase. In contrast, Lenisia cells contain multiple MROs with cristae. [7]
Breviatea is a clade of basal eukaryotes. They are closely related to the apusomonads and the Opisthokonta supergroup, and together they compose the larger clade Obazoa, which is the sister group to Amoebozoa. [3] Within Breviatea, the four known species are distributed into smaller clades of two species each: one uniting Breviata with Subulatomonas , and one uniting Lenisia with Pygsuia . [4]
Podiata |
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The class Breviatea was created in 2004 by British protozoologist Thomas Cavalier-Smith to group a problematic taxon previously known as ‘Mastigamoeba invertens’. This organism, initially classified in the Archamoebae within phylum Amoebozoa, appeared to strongly diverge in phylogenetic trees based on ribosomal RNA and had a structure very different from other Archamoebae. Because of these results, ‘M. invertens’ was separated into the order Breviatida, contained in the monotypic class Breviatea. [1] The organism was eventually renamed Breviata anathema . [8] A family-level rank for these amoebae, Breviatidae, was formally described by the same author in 2013. [2]
There are currently four accepted genera, each containing only one species.
Excavata is an extensive and diverse but possibly paraphyletic group of unicellular Eukaryota. The group was first suggested by Simpson and Patterson in 1999 and the name latinized and assigned a rank by Thomas Cavalier-Smith in 2002. It contains a variety of free-living and symbiotic protists, and includes some important parasites of humans such as Giardia and Trichomonas. Excavates were formerly considered to be included in the now obsolete Protista kingdom. They were distinguished from other lineages based on electron-microscopic information about how the cells are arranged. They are considered to be a basal flagellate lineage.
Amoebozoa is a major taxonomic group containing about 2,400 described species of amoeboid protists, often possessing blunt, fingerlike, lobose pseudopods and tubular mitochondrial cristae. In traditional classification schemes, Amoebozoa is usually ranked as a phylum within either the kingdom Protista or the kingdom Protozoa. In the classification favored by the International Society of Protistologists, it is retained as an unranked "supergroup" within Eukaryota. Molecular genetic analysis supports Amoebozoa as a monophyletic clade. Modern studies of eukaryotic phylogenetic trees identify it as the sister group to Opisthokonta, another major clade which contains both fungi and animals as well as several other clades comprising some 300 species of unicellular eukaryotes. Amoebozoa and Opisthokonta are sometimes grouped together in a high-level taxon, variously named Unikonta, Amorphea or Opimoda.
The metamonads are a large group of flagellate amitochondriate microscopic eukaryotes. Their composition is not entirely settled, but they include the retortamonads, diplomonads, and possibly the parabasalids and oxymonads as well. These four groups are all anaerobic, occurring mostly as symbiotes or parasites of animals, as is the case with Giardia lamblia which causes diarrhea in mammals.
Pelomyxa is a genus of giant flagellar amoebae, usually 500-800 μm but occasionally up to 5 mm in length, found in anaerobic or microaerobic bottom sediments of stagnant freshwater ponds or slow-moving streams.
The Apusozoa are a paraphyletic phylum of flagellate eukaryotes. They are usually around 5–20 μm in size, and occur in soils and aquatic habitats, where they feed on bacteria. They are grouped together based on the presence of an organic shell or theca under the dorsal surface of the cell.
A mitosome is an organelle found in some unicellular eukaryotic organisms, like in members of the supergroup Excavata. The mitosome was found and named in 1999, and its function has not yet been well characterized. It was termed a crypton by one group, but that name is no longer in use.
The Archamoebae are a group of protists originally thought to have evolved before the acquisition of mitochondria by eukaryotes. They include genera that are internal parasites or commensals of animals. A few species are human pathogens, causing diseases such as amoebic dysentery. The other genera of archamoebae live in freshwater habitats and are unusual among amoebae in possessing flagella. Most have a single nucleus and flagellum, but the giant amoeba Pelomyxa has many of each.
Eumycetozoa, or true slime molds, is a diverse group of protists that behave as slime molds and develop fruiting bodies, either as sorocarps or as sporocarps. It is a monophyletic group or clade within the phylum Amoebozoa that contains the myxogastrids, dictyostelids and protosporangiids.
Henneguya zschokkei or Henneguya salminicola is a species of a myxosporean endoparasite. It afflicts several salmon in the genus Oncorhynchus. It causes milky flesh or tapioca disease. H. zschokkei is notable for its lack of mitochondria, mitochondrial DNA, aerobic respiration and its reliance on an exclusively anaerobic metabolism.
A protist or protoctist is any eukaryotic organism that is not an animal, plant, or fungus. Protists do not form a natural group, or clade, but an artificial grouping of several independent clades that evolved from the last eukaryotic common ancestor.
Breviata anathema is a single-celled flagellate amoeboid eukaryote, previously studied under the name Mastigamoeba invertens. The cell lacks mitochondria, but has remnant mitochondrial genes, and possesses an organelle believed to be a modified anaerobic mitochondrion, similar to the mitosomes and hydrogenosomes found in other eukaryotes that live in low-oxygen environments.
Conosa is a grouping of Amoebozoa. It is subdivided into three groups: Archamoeba, Variosea and Mycetozoa.
Mastigamoeba is a genus of pelobionts, and treated by some as members of the Archamoebae group of protists. Mastigamoeba are characterized as anaerobic, amitochondriate organisms that are polymorphic. Their dominant life cycle stage is as an amoeboid flagellate. Species are typically free living, though endobiotic species have been described.
The apusomonads are a group of protozoan zooflagellates that glide on surfaces, and mostly consume prokaryotes. They are of particular evolutionary interest because they appear to be the sister group to the Opisthokonts, the clade that includes both animals and fungi. Together with the Breviatea, these form the Obazoa clade.
The initial version of a classification system of life by British zoologist Thomas Cavalier-Smith appeared in 1978. This initial system continued to be modified in subsequent versions that were published until he died in 2021. As with classifications of others, such as Carl Linnaeus, Ernst Haeckel, Robert Whittaker, and Carl Woese, Cavalier-Smith's classification attempts to incorporate the latest developments in taxonomy., Cavalier-Smith used his classifications to convey his opinions about the evolutionary relationships among various organisms, principally microbial. His classifications complemented his ideas communicated in scientific publications, talks, and diagrams. Different iterations might have a wider or narrow scope, include different groupings, provide greater or lesser detail, and place groups in different arrangements as his thinking changed. His classifications has been a major influence in the modern taxonomy, particularly of protists.
Varisulca was a proposed basal Podiate taxon. It encompassed several lineages of heterotrophic protists, most notably the ancyromonads (planomonads), collodictyonids (diphylleids), rigifilids and mantamonadids. Recent evidence suggests that the latter three are closely related to each other, forming a clade called CRuMs, but that this is unlikely to be specifically related to ancyromonads
Obazoa is a proposed sister clade of Amoebozoa. The term Obazoa is based on the OBA acronym for Opisthokonta, Breviatea, and Apusomonadida, the group's three constituent clades.
Anaeramoeba is a genus of anaerobic protists on uncertain phylogenetic position, first described in 2016.
A supergroup, in evolutionary biology, is a large group of organisms that share one common ancestor and have important defining characteristics. It is an informal, mostly arbitrary rank in biological taxonomy that is often greater than phylum or kingdom, although some supergroups are also treated as phyla.
Evosea is a diverse clade of amoeboid protists discovered through molecular analyses. Along with Tubulinea and Discosea, Evosea is one of the three major groups within Amoebozoa, an important clade of eukaryotic organisms. It contains unicellular organisms that display a wide variety of life cycles and cell shapes, including amoebae, flagellates and different kinds of slime molds.