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In biology, a kingdom is the second highest taxonomic rank, just below domain. Kingdoms are divided into smaller groups called phyla.
Excavata is a former supergroup of unicellular organisms belonging to the domain Eukaryota. It was first suggested by Simpson and Patterson in 1999 and introduced by Thomas Cavalier-Smith in 2002 as a formal taxon. It contains a variety of free-living and symbiotic forms, 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 classified based on their flagellar structures, and were considered to be the most basal flagellate lineage.
Chromista is a proposed but possibly polyphyletic biological kingdom consisting of single-celled and multicellular eukaryotic species that share similar features in their photosynthetic organelles (plastids). It includes all "protists" whose plastids are surrounded by four membranes and contain chlorophyll c, such as some "algae", diatoms, oomycetes, and certain "protozoans". As it is assumed that that ancestor already possessed chloroplasts of red algal origin, the non-photosynthetic forms evolved from ancestors able to perform photosynthesis. Its members might have arisen independently as separate evolutionary groups from the last eukaryotic common ancestor.
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.
Discicristata is a proposed eukaryotic clade. It consists of Euglenozoa plus Percolozoa.
A bikont is any of the eukaryotic organisms classified in the group Bikonta. Many single-celled and multi-celled organisms are members of the group, and these, as well as the presumed ancestor, have two flagella.
The Archaeplastida are a major group of eukaryotes, comprising the photoautotrophic red algae (Rhodophyta), green algae, land plants, and the minor group glaucophytes. It also includes the non-photosynthetic lineage Rhodelphidia, a predatorial (eukaryotrophic) flagellate that is sister to the Rhodophyta, and probably the microscopic picozoans. The Archaeplastida have chloroplasts that are surrounded by two membranes, suggesting that they were acquired directly through a single endosymbiosis event by feeding on a cyanobacterium. All other groups which have chloroplasts, besides the amoeboid genus Paulinella, have chloroplasts surrounded by three or four membranes, suggesting they were acquired secondarily from red or green algae. Unlike red and green algae, glaucophytes have never been involved in secondary endosymbiosis events.
Corticata, in the classification of eukaryotes, is a clade suggested by Thomas Cavalier-Smith to encompass the eukaryote supergroups of the following two groups:
Trichozoa is a group of excavates.
Loukozoa is a proposed taxon used in some classifications of eukaryotes, consisting of the Metamonada and Malawimonadea. Ancyromonads are closely related to this group, as sister of the entire group, or as sister of the Metamonada. Amorphea may have emerged in this grouping, specifically as sister of the Malawimonads.
Jakobids are an order of free-living, heterotrophic, flagellar eukaryotes in the supergroup Excavata. They are small, and can be found in aerobic and anaerobic environments. The order Jakobida, believed to be monophyletic, consists of only twenty species at present, and was classified as a group in 1993. There is ongoing research into the mitochondrial genomes of jakobids, which are unusually large and bacteria-like, evidence that jakobids may be important to the evolutionary history of eukaryotes.
Eukaryota, whose members are known as eukaryotes, is a diverse domain of organisms whose cells have a nucleus. All animals, plants, fungi, and many unicellular organisms are eukaryotes. They constitute a major group of living things, along with the two groups of prokaryotes, the Bacteria and the Archaea.
Halvaria is a taxonomic grouping of protists that includes Alveolata and Stramenopiles (Heterokonta).
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
Haptista is a proposed group of protists made up of centrohelids and haptophytes. Phylogenomic studies indicate that Haptista, together with Ancoracysta twista, forms a sister clade to the SAR+Telonemia supergroup, but it may also be sister to the Cryptista (+Archaeplastida). It is thus one of the earliest diverging Diaphoretickes.
The Orthokaryotes are a proposed Eukaryote clade consisting of the Jakobea and the Neokaryotes. Together with its sister Discicristata it forms a basal Eukaryote clade. They are characterized by stacked Golgi, orthogonal centrioles, and two opposite posterior ciliary roots.
The neokaryotes are a proposed eukaryote clade consisting of the unikonts and the bikonts as sister of for instance the Jakobea. It arises because the Euglenozoa, Percolozoa, Tsukubea, and Jakobea are seen in this view as more basal eukaryotes. These four groups, are traditionally grouped together in the Discoba. However, the Discoba may well be paraphyletic as the neokaryotes may have emerged in them.
The Scotokaryotes (Cavalier-Smith) is a proposed basal Neokaryote clade as sister of the Diaphoretickes. Basal Scotokaryote groupings are the Metamonads, the Malawimonas and the Podiata. In this phylogeny the Discoba are sometimes seen as paraphyletic and basal Eukaryotes.
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.
Malawimonads are a small group of microorganisms with a basal position in the evolutionary tree of eukaryotes, containing only three recognized species. They're considered part of a possibly paraphyletic group known as "Excavata".
References
- ↑ T. Martin Embley, Robert P. Hirt & David M. Williams (1994). "Biodiversity at the molecular level: the domains, kingdoms and phyla of life". Philosophical Transactions of the Royal Society B: Biological Sciences . 345 (1311): 21–33. Bibcode:1994RSPTB.345...21E. doi:10.1098/rstb.1994.0083. JSTOR 56135. PMID 7972353.
- ↑ Poole, Anthony; Penny, David (21 June 2007). "Engulfed by speculation" (PDF). Nature. 447 (7147): 913. doi:10.1038/447913a. PMID 17581566. S2CID 7753492. Archived from the original (PDF) on 6 July 2011. Retrieved 15 March 2011.
- ↑ Cavalier-Smith, T. (1998). "A revised six-kingdom system of life". Biological Reviews. 73 (3): 203–66. doi:10.1111/j.1469-185X.1998.tb00030.x. PMID 9809012. S2CID 6557779.
- ↑ Al Jewari, Caesar; Baldauf, Sandra L. (2023-04-28). "An excavate root for the eukaryote tree of life". Science Advances. 9 (17): eade4973. doi:10.1126/sciadv.ade4973. ISSN 2375-2548. PMC 10146883 . PMID 37115919.
- ↑ Eme, Laura; Tamarit, Daniel; Caceres, Eva F.; et al. (2023-03-09). "Inference and reconstruction of the heimdallarchaeial ancestry of eukaryotes". bioRxiv. pp. 2023.03.07.531504. doi:10.1101/2023.03.07.531504v1.
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