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Eukaryotic organisms that cannot be classified under the kingdoms Plantae, Animalia
Animalia
or Fungi
Fungi
are sometimes grouped in the kingdom Protista.

A eukaryote (/juːˈkæri.oʊt/ or /juːˈkæriət/) is any organism whose cells have a nucleus enclosed within membranes, unlike Prokaryotes ( Bacteria
Bacteria
and Archaea).[3][4][5] Eukaryotes belong to the domain Eukaryota
Eukaryota
or Eukarya. Their name comes from the Greek εὖ (eu, "well" or "true") and κάρυον (karyon, "nut" or "kernel").[6] Eukaryotic cells also contain other membrane-bound organelles such as mitochondria and the Golgi apparatus, and in addition, some cells of plants and algae contain chloroplasts. Unlike unicellular archaea and bacteria, eukaryotes may also be multicellular and include organisms consisting of many cell types forming different kinds of tissue. Eukaryotes can reproduce both asexually through mitosis and sexually through meiosis and gamete fusion. In mitosis, one cell divides to produce two genetically identical cells. In meiosis, DNA
DNA
replication is followed by two rounds of cell division to produce four haploid daughter cells. These act as sex cells (gametes). Each gamete has just one set of chromosomes, each a unique mix of the corresponding pair of parental chromosomes resulting from genetic recombination during meiosis. The domain Eukaryota
Eukaryota
appears to be monophyletic, and makes up one of the domains of life in the three-domain system. The two other domains, Bacteria
Bacteria
and Archaea, are prokaryotes[7] and have none of the above features. Eukaryotes represent a tiny minority of all living things.[8] However, due to their generally much larger size, their collective worldwide biomass is estimated to be about equal to that of prokaryotes.[8] Eukaryotes evolved approximately 1.6–2.1 billion years ago, during the Proterozoic
Proterozoic
eon.

Contents

1 History 2 Cell features

2.1 Internal membrane 2.2 Mitochondria
Mitochondria
and plastids 2.3 Cytoskeletal structures 2.4 Cell wall

3 Differences among eukaryotic cells

3.1 Animal
Animal
cell 3.2 Plant
Plant
cell 3.3 Fungal cell 3.4 Other eukaryotic cells

4 Reproduction 5 Classification

5.1 Phylogeny

5.1.1 Five supergroups 5.1.2 Cavalier-Smith's tree

6 Origin of eukaryotes

6.1 Fossils 6.2 Relationship to Archaea 6.3 Endomembrane system
Endomembrane system
and mitochondria 6.4 Hypotheses

6.4.1 Autogenous models 6.4.2 Chimeric models

7 See also 8 References 9 External links

History[edit]

Konstantin Mereschkowski
Konstantin Mereschkowski
proposed a symbiotic origin for cells with nuclei.

In 1905 and 1910, the Russian biologist Konstantin Mereschkowski (1855–1921) argued that plastids were reduced cyanobacteria in a symbiosis with a non-photosynthetic (heterotrophic) host that was itself formed by symbiosis between an amoeba-like host and a bacterium-like cell that formed the nucleus. Plants had thus inherited photosynthesis from cyanobacteria.[9] The concept of the eukaryote has been attributed to the French biologist Edouard Chatton
Edouard Chatton
(1883-1947). The terms prokaryote and eukaryote were more definitively reintroduced by the Canadian microbiologist Roger Stanier
Roger Stanier
and the Dutch-American microbiologist C. B. van Niel in 1962. In his 1938 work Titres et Travaux Scientifiques, Chatton had proposed the two terms, calling the bacteria prokaryotes and organisms with nuclei in their cells eukaryotes. However he mentioned this in only one paragraph, and the idea was effectively ignored until Chatton's statement was rediscovered by Stanier and van Niel.[10] In 1967, Lynn Margulis
Lynn Margulis
provided microbiological evidence for endosymbiosis as the origin of chloroplasts and mitochondria in eukaryotic cells in her paper, On the origin of mitosing cells.[11] In the 1970s, Carl Woese
Carl Woese
explored microbial phylogenetics, studying variations in 16S ribosomal RNA. This helped to uncover the origin of the eukaryotes and the symbiogenesis of two important eukaryote organelles, mitochondria and chloroplasts. In 1977, Woese and George Fox introduced a "third form of life", which they called the Archaebacteria; in 1990, Woese, Otto Kandler and Mark L. Wheeler renamed this the Archaea.[10] In 1979, G. W. Gould and G. J. Dring suggested that the eukaryotic cell's nucleus came from the ability of Gram-positive bacteria
Gram-positive bacteria
to form endospores. In 1987 and later papers, Thomas Cavalier-Smith
Thomas Cavalier-Smith
proposed instead that the membranes of the nucleus and endoplasmic reticulum first formed by infolding a prokaryote's plasma membrane. In the 1990s, several other biologists proposed endosymbiotic origins for the nucleus, effectively reviving Mereschkowsky's theory.[9] Cell features[edit] Eukaryotic cells are typically much larger than those of prokaryotes having a volume of around 10,000 times greater than the prokaryotic cell.[12] They have a variety of internal membrane-bound structures, called organelles, and a cytoskeleton composed of microtubules, microfilaments, and intermediate filaments, which play an important role in defining the cell's organization and shape. Eukaryotic DNA
DNA
is divided into several linear bundles called chromosomes, which are separated by a microtubular spindle during nuclear division. Internal membrane[edit]

The endomembrane system and its components

Eukaryote
Eukaryote
cells include a variety of membrane-bound structures, collectively referred to as the endomembrane system.[13] Simple compartments, called vesicles and vacuoles, can form by budding off other membranes. Many cells ingest food and other materials through a process of endocytosis, where the outer membrane invaginates and then pinches off to form a vesicle.[14] It is probable that most other membrane-bound organelles are ultimately derived from such vesicles. Alternatively some products produced by the cell can leave in a vesicle through exocytosis. The nucleus is surrounded by a double membrane (commonly referred to as a nuclear membrane or nuclear envelope), with pores that allow material to move in and out.[15] Various tube- and sheet-like extensions of the nuclear membrane form the endoplasmic reticulum, which is involved in protein transport and maturation. It includes the rough endoplasmic reticulum where ribosomes are attached to synthesize proteins, which enter the interior space or lumen. Subsequently, they generally enter vesicles, which bud off from the smooth endoplasmic reticulum.[16] In most eukaryotes, these protein-carrying vesicles are released and further modified in stacks of flattened vesicles (cisternae), the Golgi apparatus.[17] Vesicles may be specialized for various purposes. For instance, lysosomes contain digestive enzymes that break down most biomolecules in the cytoplasm.[18] Peroxisomes are used to break down peroxide, which is otherwise toxic. Many protozoans have contractile vacuoles, which collect and expel excess water, and extrusomes, which expel material used to deflect predators or capture prey. In higher plants, most of a cell's volume is taken up by a central vacuole, which mostly contains water and primarily maintains its osmotic pressure. Mitochondria
Mitochondria
and plastids[edit]

Simplified structure of a mitochondrion

Mitochondria
Mitochondria
are organelles found in nearly all eukaryotes that provide energy to the cell by converting sugars into ATP.[19] They have two surrounding membranes (each a phospholipid bi-layer), the inner of which is folded into invaginations called cristae, where aerobic respiration takes place. Mitochondria
Mitochondria
contain their own DNA. They are now generally held to have developed from endosymbiotic prokaryotes, probably proteobacteria. Protozoa
Protozoa
and microbes that lack mitochondria, such as the amoebozoan Pelomyxa
Pelomyxa
and metamonads such as Giardia
Giardia
and Trichomonas, have usually been found to contain mitochondrion-derived organelles, such as hydrogenosomes and mitosomes, and thus probably lost the mitochondria secondarily. They obtain energy by enzymatic action on nutrients absorbed from the environment. The metamonad Monocercomonoides has also acquired, by lateral gene transfer, a cytosolic sulphur mobilisation system which provides the clusters of iron and sulfur required for protein synthesis. The normal mitochondrial iron-sulphur cluster pathway has been lost secondarily.[20][21] Plants and various groups of algae also have plastids. Plastids have their own DNA
DNA
and are developed from endosymbionts, in this case cyanobacteria. They usually take the form of chloroplasts, which like cyanobacteria contain chlorophyll and produce organic compounds (such as glucose) through photosynthesis. Others are involved in storing food. Although plastids probably had a single origin, not all plastid-containing groups are closely related. Instead, some eukaryotes have obtained them from others through secondary endosymbiosis or ingestion.[22] The capture and sequestering of photosynthetic cells and chloroplasts occurs in many types of modern eukaryotic organisms and is known as kleptoplasty. Endosymbiotic origins have also been proposed for the nucleus, and for eukaryotic flagella.[23] Cytoskeletal structures[edit] Main article: Cytoskeleton

Longitudinal section through the flagellum of Chlamydomonas reinhardtii

Many eukaryotes have long slender motile cytoplasmic projections, called flagella, or similar structures called cilia. Flagella and cilia are sometimes referred to as undulipodia,[24] and are variously involved in movement, feeding, and sensation. They are composed mainly of tubulin. These are entirely distinct from prokaryotic flagellae. They are supported by a bundle of microtubules arising from a centriole, characteristically arranged as nine doublets surrounding two singlets. Flagella also may have hairs, or mastigonemes, and scales connecting membranes and internal rods. Their interior is continuous with the cell's cytoplasm. Microfilamental structures composed of actin and actin binding proteins, e.g., α-actinin, fimbrin, filamin are present in submembraneous cortical layers and bundles, as well. Motor proteins of microtubules, e.g., dynein or kinesin and actin, e.g., myosins provide dynamic character of the network. Centrioles
Centrioles
are often present even in cells and groups that do not have flagella, but conifers and flowering plants have neither. They generally occur in groups that give rise to various microtubular roots. These form a primary component of the cytoskeletal structure, and are often assembled over the course of several cell divisions, with one flagellum retained from the parent and the other derived from it. Centrioles
Centrioles
produce the spindle during nuclear division.[25] The significance of cytoskeletal structures is underlined in the determination of shape of the cells, as well as their being essential components of migratory responses like chemotaxis and chemokinesis. Some protists have various other microtubule-supported organelles. These include the radiolaria and heliozoa, which produce axopodia used in flotation or to capture prey, and the haptophytes, which have a peculiar flagellum-like organelle called the haptonema. Cell wall[edit] Main article: Cell wall The cells of plants and algae, fungi and most chromalveolates have a cell wall, a layer outside the cell membrane, providing the cell with structural support, protection, and a filtering mechanism. The cell wall also prevents over-expansion when water enters the cell.[26] The major polysaccharides making up the primary cell wall of land plants are cellulose, hemicellulose, and pectin. The cellulose microfibrils are linked via hemicellulosic tethers to form the cellulose-hemicellulose network, which is embedded in the pectin matrix. The most common hemicellulose in the primary cell wall is xyloglucan.[27] Differences among eukaryotic cells[edit] There are many different types of eukaryotic cells, though animals and plants are the most familiar eukaryotes, and thus provide an excellent starting point for understanding eukaryotic structure. Fungi
Fungi
and many protists have some substantial differences, however. Animal
Animal
cell[edit]

Structure of a typical animal cell

Structure of a typical plant cell

All animals are eukaryotic. Animal
Animal
cells are distinct from those of other eukaryotes, most notably plants, as they lack cell walls and chloroplasts and have smaller vacuoles. Due to the lack of a cell wall, animal cells can adopt a variety of shapes. A phagocytic cell can even engulf other structures. Plant
Plant
cell[edit] Main article: Plant
Plant
cell Plant
Plant
cells are quite different from the cells of the other eukaryotic organisms. Their distinctive features are:

A large central vacuole (enclosed by a membrane, the tonoplast), which maintains the cell's turgor and controls movement of molecules between the cytosol and sap[28] A primary cell wall containing cellulose, hemicellulose and pectin, deposited by the protoplast on the outside of the cell membrane; this contrasts with the cell walls of fungi, which contain chitin, and the cell envelopes of prokaryotes, in which peptidoglycans are the main structural molecules The plasmodesmata, pores in the cell wall that link adjacent cells and allow plant cells to communicate with adjacent cells.[29] Animals have a different but functionally analogous system of gap junctions between adjacent cells. Plastids, especially chloroplasts that contain chlorophyll, the pigment that gives plants their green color and allows them to perform photosynthesis Bryophytes and seedless vascular plants only have flagellae and centrioles in the sperm cells.[30] Sperm of cycads and Ginkgo
Ginkgo
are large, complex cells that swim with hundreds to thousands of flagellae.[31] Conifers (Pinophyta) and flowering plants (Angiospermae) lack the flagellae and centrioles that are present in animal cells.

Fungal cell[edit]

Fungal Hyphae Cells 1- Hyphal wall 2- Septum
Septum
3- Mitochondrion
Mitochondrion
4- Vacuole
Vacuole
5- Ergosterol crystal 6- Ribosome
Ribosome
7- Nucleus 8- Endoplasmic reticulum
Endoplasmic reticulum
9- Lipid body 10- Plasma membrane
Plasma membrane
11- Spitzenkörper 12- Golgi apparatus

The cells of fungi are most similar to animal cells, with the following exceptions:[32]

A cell wall that contains chitin Less definition between cells; the hyphae of higher fungi have porous partitions called septa, which allow the passage of cytoplasm, organelles, and, sometimes, nuclei. Primitive fungi have few or no septa, so each organism is essentially a giant multinucleate supercell; these fungi are described as coenocytic. Only the most primitive fungi, chytrids, have flagella.

Other eukaryotic cells[edit] Some groups of eukaryotes have unique organelles, such as the cyanelles (unusual chloroplasts) of the glaucophytes,[33] the haptonema of the haptophytes, or the ejectosomes of the cryptomonads. Other structures, such as pseudopodia, are found in various eukaryote groups in different forms, such as the lobose amoebozoans or the reticulose foraminiferans.[34] Reproduction[edit]

This diagram illustrates the twofold cost of sex. If each individual were to contribute to the same number of offspring (two), (a) the sexual population remains the same size each generation, where the (b) asexual population doubles in size each generation.

Cell division
Cell division
generally takes place asexually by mitosis, a process that allows each daughter nucleus to receive one copy of each chromosome. Most eukaryotes also have a life cycle that involves sexual reproduction, alternating between a haploid phase, where only one copy of each chromosome is present in each cell and a diploid phase, wherein two copies of each chromosome are present in each cell. The diploid phase is formed by fusion of two haploid gametes to form a zygote, which may divide by mitosis or undergo chromosome reduction by meiosis. There is considerable variation in this pattern. Animals have no multicellular haploid phase, but each plant generation can consist of haploid and diploid multicellular phases. Eukaryotes have a smaller surface area to volume ratio than prokaryotes, and thus have lower metabolic rates and longer generation times.[35] The evolution of sexual reproduction may be a primordial and fundamental characteristic of eukaryotes. Based on a phylogenetic analysis, Dacks and Roger proposed that facultative sex was present in the common ancestor of all eukaryotes.[36] A core set of genes that function in meiosis is present in both Trichomonas
Trichomonas
vaginalis and Giardia
Giardia
intestinalis, two organisms previously thought to be asexual.[37][38] Since these two species are descendants of lineages that diverged early from the eukaryotic evolutionary tree, it was inferred that core meiotic genes, and hence sex, were likely present in a common ancestor of all eukaryotes.[37][38] Eukaryotic species once thought to be asexual, such as parasitic protozoa of the genus Leishmania, have been shown to have a sexual cycle.[39] Also, evidence now indicates that amoebae, previously regarded as asexual, are anciently sexual and that the majority of present-day asexual groups likely arose recently and independently.[40] Classification[edit] Further information: wikispecies:Eukaryota

Phylogenetic and symbiogenetic tree of living organisms, showing a view of the origins of eukaryotes & prokaryotes

One hypothesis of eukaryotic relationships. The Opisthokonta
Opisthokonta
group includes both animals (Metazoa) and fungi. Plants (Plantae) are placed in Archaeplastida.

A pie chart of described eukaryote species (except for Excavata), together with a tree showing possible relationships between the groups

In antiquity, the two lineages of animals and plants were recognized. They were given the taxonomic rank of Kingdom by Linnaeus. Though he included the fungi with plants with some reservations, it was later realized that they are quite distinct and warrant a separate kingdom, the composition of which was not entirely clear until the 1980s.[41] The various single-cell eukaryotes were originally placed with plants or animals when they became known. In 1830, the German biologist Georg A. Goldfuss coined the word protozoa to refer to organisms such as ciliates, and this group was expanded until it encompassed all single-celled eukaryotes, and given their own kingdom, the Protista, by Ernst Haeckel
Ernst Haeckel
in 1866.[42][43] The eukaryotes thus came to be composed of four kingdoms:

Kingdom Protista Kingdom Plantae Kingdom Fungi Kingdom Animalia

The protists were understood to be "primitive forms", and thus an evolutionary grade, united by their primitive unicellular nature.[43] The disentanglement of the deep splits in the tree of life only really started with DNA
DNA
sequencing, leading to a system of domains rather than kingdoms as top level rank being put forward by Carl Woese, uniting all the eukaryote kingdoms under the eukaryote domain.[44] At the same time, work on the protist tree intensified, and is still actively going on today. Several alternative classifications have been forwarded, though there is no consensus in the field. A classification produced in 2005 for the International Society of Protistologists,[45] which reflected the consensus of the time, divided the eukaryotes into six supposedly monophyletic 'supergroups'. However, in the same year (2005), doubts were expressed as to whether some of these supergroups were monophyletic, particularly the Chromalveolata,[46] and a review in 2006 noted the lack of evidence for several of the supposed six supergroups.[47] A revised classification in 2012[2] recognizes five supergroups.

Archaeplastida
Archaeplastida
(or Primoplantae) Land plants, green algae, red algae, and glaucophytes

SAR supergroup Stramenopiles
Stramenopiles
(brown algae, diatoms, etc.), Alveolata, and Rhizaria (Foraminifera, Radiolaria, and various other amoeboid protozoa).

Excavata Various flagellate protozoa

Amoebozoa Most lobose amoeboids and slime molds

Opisthokonta Animals, fungi, choanoflagellates, etc.

There are also smaller groups of eukaryotes whose position is uncertain or seems to fall outside the major groups[48] — in particular, Haptophyta, Cryptophyta, Centrohelida, Telonemia, Picozoa,[49] Apusomonadida, Ancyromonadida, Breviatea, and the genus Collodictyon.[50] Overall, it seems that, although progress has been made, there are still very significant uncertainties in the evolutionary history and classification of eukaryotes. As Roger & Simpson said in 2009 "with the current pace of change in our understanding of the eukaryote tree of life, we should proceed with caution."[51] In an article published in Nature Microbiology in April 2016 the authors, "reinforced once again that the life we see around us – plants, animals, humans and other so-called eukaryotes – represent a tiny percentage of the world's biodiversity."[52] They classified eukaryote "based on the inheritance of their information systems as opposed to lipid or other cellular structures." Jillian F. Banfield of the University of California, Berkeley
University of California, Berkeley
and fellow scientists used a super computer to generate a diagram of a new tree of life based on DNA
DNA
from 3000 species including 2,072 known species and 1,011 newly reported microbial organisms, whose DNA
DNA
they had gathered from diverse environments.[7][53] As the capacity to sequence DNA
DNA
became easier, Banfield and team were able to do metagenomic sequencing—"sequencing whole communities of organisms at once and picking out the individual groups based on their genes alone."[52] Phylogeny[edit] The rRNA trees constructed during the 1980s and 1990s left most eukaryotes in an unresolved "crown" group (not technically a true crown), which was usually divided by the form of the mitochondrial cristae; see crown eukaryotes. The few groups that lack mitochondria branched separately, and so the absence was believed to be primitive; but this is now considered an artifact of long-branch attraction, and they are known to have lost them secondarily.[54][55] As of 2011[update], there is widespread agreement that the Rhizaria belong with the Stramenopiles
Stramenopiles
and the Alveolata, in a clade dubbed the SAR supergroup, so that Rhizaria
Rhizaria
is not one of the main eukaryote groups; also that the Amoebozoa
Amoebozoa
and Opisthokonta
Opisthokonta
are each monophyletic and form a clade, often called the unikonts.[56][57][58][59][60] Beyond this, there does not appear to be a consensus. It has been estimated that there may be 75 distinct lineages of eukaryotes.[61] Most of these lineages are protists. The known eukaryote genome sizes vary from 8.2 megabases (Mb) in Babesia bovis to 112,000–220,050 Mb in the dinoflagellate Prorocentrum
Prorocentrum
micans, showing that the genome of the ancestral eukaryote has undergone considerable variation during its evolution.[61] The last common ancestor of all eukaryotes is believed to have been a phagotrophic protist with a nucleus, at least one centriole and cilium, facultatively aerobic mitochondria, sex (meiosis and syngamy), a dormant cyst with a cell wall of chitin and/or cellulose and peroxisomes.[61] Later endosymbiosis led to the spread of plastids in some lineages. Five supergroups[edit] A global tree of eukaryotes from a consensus of phylogenetic evidence (in particular, phylogenomics), rare genomic signatures, and morphological characteristics is presented in Adl et al. 2012[2] and Burki 2014/2016 with the Cryptophyta
Cryptophyta
and picozoa having emerged within the Archaeplastida.[48][62][63] A similar inclusion of Glaucophyta, Cryptista
Cryptista
(and also Haptista) is recovered in Karnkowska et al.[64]

Eukaryotes

Diaphoretickes

Archaeplastida

Red algae
Red algae
(Rhodophyta)

picozoa

Glaucophyta
Glaucophyta

Green plants
Green plants
(Viridiplantae)

Cryptista

Haptista

Ancoracysta

Telonemia

SAR

Halvaria

Stramenopiles
Stramenopiles

Alveolata
Alveolata

Rhizaria
Rhizaria

Discoba
Discoba

Amorphea

Amoebozoa
Amoebozoa

Apusomonadida
Apusomonadida

Opisthokonta

Holomycota
Holomycota
(inc. fungi)

Holozoa
Holozoa
(inc. animals)

In some analyses, the Hacrobia
Hacrobia
group ( Haptophyta
Haptophyta
+ Cryptophyta) is placed next to Archaeplastida,[56] but in other ones it is nested inside the Archaeplastida.[65] However, several recent studies have concluded that Haptophyta
Haptophyta
and Cryptophyta
Cryptophyta
do not form a monophyletic group.[66] The former could be a sister group to the SAR group, the latter cluster with the Archaeplastida
Archaeplastida
(plants in the broad sense).[67] The division of the eukaryotes into two primary clades, bikonts ( Archaeplastida
Archaeplastida
+ SAR + Excavata) and unikonts ( Amoebozoa
Amoebozoa
+ Opisthokonta), derived from an ancestral biflagellar organism and an ancestral uniflagellar organism, respectively, had been suggested earlier.[65][68][69] A 2012 study produced a somewhat similar division, although noting that the terms "unikonts" and "bikonts" were not used in the original sense.[49] A highly converged and congruent set of trees appears in Derelle et al (2015), Ren et al (2016), Yang et al (2017) and Cavalier-Smith (2015) including the supplementary information, resulting in a more conservative and consolidated tree. It is combined with some results from Cavalier-Smith for the basal Opimoda.[70][71][72][73][74][75][76] The main remaining controversies are the root, and the exact positioning of the Rhodophyta
Rhodophyta
and the bikonts Rhizaria, Haptista, Cryptista, Picozoa and Telonemia, many of which may be eukaryote-eukaryote hybrids.[77] Archeaplastida developed the Chloroplasts probably by endosymbiosis of an ancestor related to a currently extant cyanobacterium, Gloeomargarita lithophora.[78][79][77]

Eukaryotes

Diphoda

Diaphoretickes

Archaeplastida

Glaucophyta

Rhodophyta

Viridiplantae

 (+ Gloeomargarita lithophora) 

Hacrobia

Haptista

Cryptista

SAR

Halvaria

Stramenopiles

Alveolata

Rhizaria

Discoba

Opimoda

Metamonada

Ancyromonas

Malawimonas

Podiata

CRuMs

Diphyllatea, Rigifilida, Mantamonas

Amorphea

Amoebozoa

Obazoa

Breviata

Apusomonadida

Opisthokonta

Cavalier-Smith's tree[edit] Thomas Cavalier-Smith
Thomas Cavalier-Smith
2010,[80] 2013,[81] 2014[82] and 2017[83] places the eukaryotic tree's root between Excavata
Excavata
(with ventral feeding groove supported by a microtubular root) and the grooveless Euglenozoa, and monophyletic Chromista, correlated to a single endosymbyotic event of capturing a red-algae.

Eukaryotes

Tsukubea

Discicristata

Euglenozoa

Percolozoa

Orthokaryota

Jakobea

Neokaryota

Corticata

Plantae

Glaucophytes

Rhodophytes

Viridiplantae

Chromista  (+ Rhodophyte) 

Hacrobia

SAR

Scotokaryota

Metamonada

Opimoda

Malawimonadea

Podiata

Ancyromonadida

Mantamonadia

Diphyllatea

Amorphea

Amoebozoa

Obazoa

Breviatea

Apusomonadida

Opisthokonta

Origin of eukaryotes[edit]

The three-domains tree and the Eocyte hypothesis[84]

Phylogenetic tree
Phylogenetic tree
showing a possible relationship between the eukaryotes and other forms of life;[85] eukaryotes are colored red, archaea green and bacteria blue.

Fossils[edit] The origin of the eukaryotic cell is a milestone in the evolution of life, since eukaryotes include all complex cells and almost all multicellular organisms. The timing of this series of events is hard to determine; Knoll (2006) suggests they developed approximately 1.6–2.1 billion years ago. Some acritarchs are known from at least 1.65 billion years ago, and the possible alga Grypania
Grypania
has been found as far back as 2.1 billion years ago.[86] The Geosiphon-like fossil fungus Diskagma
Diskagma
has been found in paleosols 2.2 billion years old.[87] Organized living structures have been found in the black shales of the Palaeoproterozoic Francevillian B Formation in Gabon, dated at 2.1 billion years old. Eukaryotic life could have evolved at that time.[88] Fossils that are clearly related to modern groups start appearing an estimated 1.2 billion years ago, in the form of a red alga, though recent work suggests the existence of fossilized filamentous algae in the Vindhya
Vindhya
basin dating back perhaps to 1.6 to 1.7 billion years ago.[89] Biomarkers suggest that at least stem eukaryotes arose even earlier. The presence of steranes in Australian shales indicates that eukaryotes were present in these rocks dated at 2.7 billion years old.[90][91] Relationship to Archaea[edit] The nuclear DNA
DNA
and genetic machinery of eukaryotes is more similar to Archaea
Archaea
than Bacteria, leading to a controversial suggestion that eukaryotes should be grouped with Archaea
Archaea
in the clade Neomura. In other respects, such as membrane composition, eukaryotes are similar to Bacteria. Three main explanations for this have been proposed:

Eukaryotes resulted from the complete fusion of two or more cells, wherein the cytoplasm formed from a eubacterium, and the nucleus from an archaeon,[92] from a virus,[93][94] or from a pre-cell.[95][96] Eukaryotes developed from Archaea, and acquired their eubacterial characteristics through the endosymbiosis of a proto-mitochondrion of eubacterial origin.[97] Eukaryotes and Archaea
Archaea
developed separately from a modified eubacterium.

Diagram of the origin of life with the Eukaryotes appearing early, not derived from Prokaryotes, as proposed by Richard Egel in 2012. This view implies that the UCA was relatively large and complex.[98]

Alternative proposals include:

The chronocyte hypothesis postulates that a primitive eukaryotic cell was formed by the endosymbiosis of both archaea and bacteria by a third type of cell, termed a chronocyte.[99] The universal common ancestor (UCA) of the current tree of life was a complex organism that survived a mass extinction event rather than an early stage in the evolution of life. Eukaryotes and in particular akaryotes ( Bacteria
Bacteria
and Archaea) evolved through reductive loss,[100] so that similarities result from differential retention of original features.

Assuming no other group is involved, there are three possible phylogenies for the Bacteria, Archaea
Archaea
and Eukaryota
Eukaryota
in which each is monophyletic. These are labelled 1 to 3 in the table below. The eocyte hypothesis is a modification of hypothesis 2 in which the Archaea
Archaea
are paraphyletic. (The table and the names for the hypotheses are based on Harish and Kurland, 2017.[101])

Alternative hypotheses for the base of the tree of life

1 – Two empires 2 – Three domains 3 – Gupta 4 – Eocyte

UCA 

Archaea

Bacteria

Eukaryota

UCA 

Eukaryota

Archaea

Bacteria

UCA 

Eukaryota

Bacteria

Archaea

UCA 

Eukaryota

Archaea-Crenarchaeota

Archaea-Euryarchaeota

Bacteria

In recent years, most researchers have favoured either the three domains (3D) or the eocyte hypotheses. An rRNA analyses supports the eocyte scenario, apparently with the Eukaryote
Eukaryote
root in Excavata.[102][80][81][82][83] A cladogram supporting the eocyte hypothesis, positioning eukaryotes within Archaea, based on phylogenomic analyses of the Asgard archaea, is:[103][104]

Proteoarchaeota

TACK

Korarchaeota

Crenarchaeota

Aigarchaeota

Geoarchaeota

Thaumarchaeota

Bathyarchaeota

Asgard

Lokiarchaeota

Odinarchaeota

Thorarchaeota

Heimdallarchaeota

(+α─Proteobacteria)

Eukaryota

In this scenario, the Asgard group is seen as a sister taxon of the TACK
TACK
group, which comprises Crenarchaeota
Crenarchaeota
(formerly named eocytes), Thaumarchaeota, and others. In 2017, there has been significant pushback against this scenario, arguing that the eukaryotes did not emerge within the Archaea. Cunha et al. produced analyses supporting the three domains (3D) or Woese hypothesis (2 in the table above) and rejecting the eocyte hypothesis (4 above).[105] Harish and Kurland found strong support for the earlier two empires (2D) or Mayr hypothesis (1 in the table above), based on analyses of the coding sequences of protein domains. They rejected the eocyte hypothesis as the least likely.[106][101] A possible interpretation of their analysis is that the universal common ancestor (UCA) of the current tree of life was a complex organism that survived an evolutionary bottleneck, rather than a simpler organism arising early in the history of life.[100] Endomembrane system
Endomembrane system
and mitochondria[edit] The origins of the endomembrane system and mitochondria are also unclear.[107] The phagotrophic hypothesis proposes that eukaryotic-type membranes lacking a cell wall originated first, with the development of endocytosis, whereas mitochondria were acquired by ingestion as endosymbionts.[108] The syntrophic hypothesis proposes that the proto-eukaryote relied on the proto-mitochondrion for food, and so ultimately grew to surround it. Here the membranes originated after the engulfment of the mitochondrion, in part thanks to mitochondrial genes (the hydrogen hypothesis is one particular version).[109] In a study using genomes to construct supertrees, Pisani et al. (2007) suggest that, along with evidence that there was never a mitochondrion-less eukaryote, eukaryotes evolved from a syntrophy between an archaea closely related to Thermoplasmatales and an α-proteobacterium, likely a symbiosis driven by sulfur or hydrogen. The mitochondrion and its genome is a remnant of the α-proteobacterial endosymbiont.[110] Hypotheses[edit] Different hypotheses have been proposed as to how eukaryotic cells came into existence. These hypotheses can be classified into two distinct classes – autogenous models and chimeric models. Autogenous models[edit]

An autogenous model for the origin of eukaryotes.

Autogenous models propose that a proto-eukaryotic cell containing a nucleus existed first, and later acquired mitochondria.[111] According to this model, a large prokaryote developed invaginations in its plasma membrane in order to obtain enough surface area to service its cytoplasmic volume. As the invaginations differentiated in function, some became separate compartments—giving rise to the endomembrane system, including the endoplasmic reticulum, golgi apparatus, nuclear membrane, and single membrane structures such as lysosomes.[112] Mitochondria
Mitochondria
are proposed to come from the endosymbiosis of an aerobic proteobacterium, and it is assumed that all the eukaryotic lineages that did not acquire mitochondria became extinct.[113] Chloroplasts came about from another endosymbiotic event involving cyanobacteria. Since all eukaryotes have mitochondria, but not all have chloroplasts, the serial endosymbiosis theory proposes that mitochondria came first. Chimeric models[edit] Chimeric models claim that two prokaryotic cells existed initially – an archaeon and a bacterium. These cells underwent a merging process, either by a physical fusion or by endosymbiosis, thereby leading to the formation of a eukaryotic cell. Within these chimeric models, some studies further claim that mitochondria originated from a bacterial ancestor while others emphasize the role of endosymbiotic processes behind the origin of mitochondria. Based on the process of mutualistic symbiosis, the hypotheses can be categorized as – the serial endosymbiotic theory (SET),[114][115][116] the hydrogen hypothesis (mostly a process of symbiosis where hydrogen transfer takes place among different species),[117] and the syntrophy hypothesis.[118][119] According to serial endosymbiotic theory (championed by Lynn Margulis), a union between a motile anaerobic bacterium (like Spirochaeta) and a thermoacidophilic crenarchaeon (like Thermoplasma which is sulfidogenic in nature) gave rise to the present day eukaryotes. This union established a motile organism capable of living in the already existing acidic and sulfurous waters. Oxygen is known to cause toxicity to organisms that lack the required metabolic machinery. Thus, the archaeon provided the bacterium with a highly beneficial reduced environment (sulfur and sulfate were reduced to sulfide). In microaerophilic conditions, oxygen was reduced to water thereby creating a mutual benefit platform. The bacterium on the other hand, contributed the necessary fermentation products and electron acceptors along with its motility feature to the archaeon thereby gaining a swimming motility for the organism. From a consortium of bacterial and archaeal DNA
DNA
originated the nuclear genome of eukaryotic cells. Spirochetes gave rise to the motile features of eukaryotic cells. Endosymbiotic unifications of the ancestors of alpha-proteobacteria and cyanobacteria, led to the origin of mitochondria and plastids respectively. For example, Thiodendron has been known to have originated via an ectosymbiotic process based on a similar syntrophy of sulfur existing between the two types of bacteria – Desulphobacter and Spirochaeta. However, such an association based on motile symbiosis have never been observed practically. Also there is no evidence of archaeans and spirochetes adapting to intense acid-based environments.[120] In the hydrogen hypothesis, the symbiotic linkage of an anaerobic and autotrophic methanogenic archaeon (host) with an alpha-proteobacterium (the symbiont) gave rise to the eukaryotes. The host utilized hydrogen (H2) and carbon dioxide (CO2) to produce methane while the symbiont, capable of aerobic respiration, expelled H2 and CO2 as byproducts of anaerobic fermentation process. The host's methanogenic environment worked as a sink for H2, which resulted in heightened bacterial fermentation. Endosymbiotic gene transfer (EGT) acted as a catalyst for the host to acquire the symbionts' carbohydrate metabolism and turn heterotrophic in nature. Subsequently, the host's methane forming capability was lost. Thus, the origins of the heterotrophic organelle (symbiont) are identical to the origins of the eukaryotic lineage. In this hypothesis, the presence of H2 represents the selective force that forged eukaryotes out of prokaryotes.[citation needed] The syntrophy hypothesis was developed in contrast to the hydrogen hypothesis and proposes the existence of two symbiotic events. According to this theory, the origin of eukaryotic cells was based on metabolic symbiosis (syntrophy) between a methanogenic archaeon and a delta-proteobacterium. This syntrophic symbiosis was initially facilitated by H2 transfer between different species under anaerobic environments. In earlier stages, an alpha-proteobacterium became a member of this integration, and later developed into the mitochondrion. Gene
Gene
transfer from a delta-proteobacterium to an archaeon led to the methanogenic archaeon developing into a nucleus. The archaeon constituted the genetic apparatus, while the delta-proteobacterium contributed towards the cytoplasmic features. This theory incorporates two selective forces at the time of nucleus evolution – (a) presence of metabolic partitioning to avoid the harmful effects of the co-existence of anabolic and catabolic cellular pathways, and (b) prevention of abnormal protein biosynthesis due to a vast spread of introns in the archaeal genes after acquiring the mitochondrion and losing methanogenesis.[citation needed] See also[edit]

Biology portal

Book: Eukaryote

Evolution
Evolution
of sexual reproduction List of sequenced eukaryotic genomes Parikaryote Prokaryote Thaumarchaeota Vault (organelle)

References[edit]

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 This article incorporates public domain material from the NCBI document "Science Primer".[dead link] External links[edit]

Wikispecies
Wikispecies
has information related to Eukaryota

Eukaryotes (Tree of Life
Life
web site) Eukaryote
Eukaryote
at the Encyclopedia of Life
Encyclopedia of Life

v t e

Eukaryota

Domain Archaea Bacteria Eukaryota (Supergroup Plant Hacrobia Heterokont Alveolata Rhizaria Excavata Amoebozoa Opisthokonta

Animal Fungi)

Diaphoretickes

Archaeplastida

Glaucophyta Rhodophyta

Viridiplantae Plantae
Plantae
s.s.

Chlorophyta Streptophyta

Cryptista

Corbihelia Cryptophyta

A+H

Ancoracysta twista Haptista

Centroheliozoa Haptophyta

SAR

Halvaria

Alveolata

Ciliates Miozoa

Acavomonadia Colponemidia Myzozoa

Stramenopiles (heterokonts)

Bicosoecea Developea Hyphochytrea Ochrophyta Peronosporomycota Pirsoniomycota Placidozoa Platysulcea Sagenista

Rhizaria

Filosa Phytomyxea Retaria

Ectoreta Marimyxia

Vampyrellidea

Incertae sedis

Kamera lens

Excavata

Ancyromonadida Malawimonadea Metamonada
Metamonada
(Anaeromonada, Trichozoa)

Discoba

Jakobea Tsukubea

Discicristata

Euglenozoa Percolozoa

Podiata

Amorphea

Amoebozoa

Conosa
Conosa
(Archamoebae, Semiconosia) Lobosa
Lobosa
(Cutosea, Discosea, Tubulinea)

Obazoa

Apusomonadida Breviatea

Opisthokonta

Holomycota

Cristidiscoidea Opisthosporidia

Aphelida Cryptomycota Microsporidia

True fungi

Holozoa

Choanoflagellates Filasterea Metazoa or Animals Ichthyosporea Pluriformea

Syssomonas Corallochytrea

CRuMs

Diphyllatea Mantamonadida Rigifilida Discocelida? Micronucleariida?

Incertae sedis

Parakaryon myojinensis †Acritarcha †Charnia †Gakarusia †Galaxiopsis †Grypania †Leptoteichos

Major kingdoms are underlined. See also: protist. Sources and alternative views: Wikispecies.

v t e

Excavata

Domain Archaea Bacteria Eukaryota (Supergroup Plant Hacrobia Heterokont Alveolata Rhizaria Excavata Amoebozoa Opisthokonta

Animal Fungi)

Discoba

Discicristata

Euglenozoa

Postgaardia

Postgaardea

Bihospitida

Bihospitidae

Postgaardida

Calkinsiidae Postgaardidae

Glycomonada

Diplonemea

Diplonemida

Diplonemidae Hemistasiidae

Kinetoplastea

Bordnamonadida Trypanophidida Prokinetoplastida Neobodonida Parabodonida Bodonida Trypanosomatida

Euglenida

Entosiphonea

Entosiphonida

Entosiphonidae

Stavomonadea

Heterostavida

Serpenomonadidae

Decastavida

Decastavidae Keelungiidae

Petalomonadida

Sphenomonadidae Petalomonadidae

Ploeotarea

Ploeotiida

Lentomonadidae Ploeotiidae

Peranemea

Peranemida

Pseudoperanemataceae

Anisonemida

Anisonemidae

Natomonadida

Neometanemidae Distigmidae Astasiidae

Acroglissida

Teloproctidae

Euglenophyceae

Rapazida

Rapazidae

Eutreptiales

Eutreptiaceae

Euglenales

Euglenomorphaceae Phacaceae Euglenaceae

Percolozoa

Pharyngomonadidea

Pharyngomonadida

Pharyngomonadidae

Heterolobosea

Lyromonadida

Plaesiobystridae Gruberellidae Psalteriomonadidae

Acrasida

Acrasidae Guttulinidae

Schizopyrenida

Naegleriidae Vahlkampfiidae Neovahlkampfiidae Paravahlkampfiidae Euhyperamoebidae

Percolatea

Percolomonas Stephanopogon

Jakobea

Jakobida

Andaluciidae Stygiellidae Moramonadidae Jakobidae Histionidae

Tsukubea

Tsukubamonadida

Tsukubamonadidae

Loukozoa

Metamonad

Trichozoa

Parabasalia

Chilomitea

Chilomitida

Chilomitidae

Trichonymphea

Lophomonadida

Lophomonadidae

Trichonymphida

Hoplonymphidae Spirotrichosomidae Staurojoeninidae Teranymphidae Trichonymphidae

Trichomonadea

Trichomonadida

Hypotrichomonadidae Tricercomitidae Hexamastigidae Honigbergiellidae Trichomonadidae

Trichocovinida

Trichocovinidae

Tritrichomonadida

Dientamoebidae Monocercomonadidae Simplicimonadidae Tritrichomonadidae

Spirotrichonymphida

Spirotrichonymphidae

Cristamonadida

Calonymphidae Devescovinidae

Fornicata

Eopharingea

Caviomonadidae Diplomonadida

Giardiidae Octomitidae Spironucleidae Hexamitidae

Retortamonadida

Retortamonadidae

Carpediemonadea

Carpediemonadida

Carpediemonadidae

Other

Kipferliidae Dysnectida

Dysnectidae

Chilomastigida

Chilomastigidae

Anaeromonada

Anaeromonadea

Paratrimastigidae Trimastigida

Trimastigidae

Oxymonadida

Polymastigidae Saccinobaculidae Pyrsonymphidae Streblomastigidae Oxymonadidae

Neolouka

Malawimonadea

Malawimonadida

Malawimonadidae

Ancyromonadida

Ancyromonadida

Ancyromonadida

v t e

Classification of Archaeplastida
Archaeplastida
/ Plantae
Plantae
sensu lato

Domain Archaea Bacteria Eukaryota (Supergroup Plant Hacrobia Heterokont Alveolata Rhizaria Excavata Amoebozoa Opisthokonta

Animal Fungi)

Rhodophyta (red algae)

Cyanidiophyceae Porphyridiophyceae Compsopogonophyceae Stylonematophyceae Rhodellophyceae Bangiophyceae Florideophyceae

Glaucocystophyta (glaucophytes)

Glaucocystophyceae

Glaucocystis Cyanophora Gloeochaete

Viridiplantae (green algae, & land plants)

Mesostigmatophyceae Chlorokybophyceae

C+S

Chlorophyta

Palmophyllales Nephrophyceae Prasinophyceae Pseudoscourfieldiales Pyramimonadophyceae Scourfieldiales Pedinophyceae Chlorodendrophyceae UTC clade

Ulvophyceae Trebouxiophyceae Chlorophyceae

Streptophyta (charophytes, & land plants)

Klebsormidiophyceae

Phragmo- plastophyta

Charophyceae Coleochaetophyceae Zygnematophyceae

Embryophyta (land plants)

Bryophytes (non-vascular)

Marchantiophyta Anthocerotophyta Bryophyta "Moss" †Horneophytopsida

Tracheophyta (vascular)

Lycopodiophyta (microphylls)

†Zosterophyllopsida †Sawdoniales Isoetopsida Lycopodiopsida

Euphyllophyta (megaphylls)

Moniliformopses (ferns)

†Cladoxylopsida †Stauropteridales †Zygopteridales Equisetopsida Psilotopsida Marattiopsida Polypodiopsida

Spermatophyta (seed plants)

†Seed ferns Gymnosperms

Gnetopsida Pinopsida Cycadopsida Ginkgoopsida

Angiosperms or flowering plants

Amborellales Nymphaeales Austrobaileyales Magnoliids Monocots Eudicots

Other

†Trimerophytopsida †Progymnosperm

Other

†Rhyniopsida

† = extinct. See also the list of plant orders.

v t e

Eukaryota: Hacrobia

Domain Archaea Bacteria Eukaryota (Supergroup Plant Hacrobia Heterokont Alveolata Rhizaria Excavata Amoebozoa Opisthokonta

Animal Fungi)

Cryptista

Corbihelia

Endohelea

Microhelida

Microhelidae

Heliomonadida

Heliomonadidae

Picomonadea

Picomonadida

Picomonas

Telonemea

Telonemida

Telonemidae

Cryptophyta

Palpitea

Palpitomonadida

Palpitomonas

Katablepharidea

Katablepharida

Katablepharidae

Goniomonadea

Goniomonadida

Goniomonas

Cryptophyceae

Tetragonidiales

Tetragonidiaceae

Cryptomonadales

Cryptomonadaceae

GPTgc (Plagioselmis) other (Cryptomonas/Chilomonas/Goniomonas)

Hemiselmidaceae

CKHgc (Hemiselmis)

Pyrenomonadales

Chroomonadaceae

CKHgc (Chroomonas, Komma) other (Falcomonas)

Geminigeraceae

GHgc (Guillardia, Hanusia) GPTgc (Geminigera, Teleaulax) other (Proteomonas)

Pyrenomonadaceae

RRSgc (Pyrenomonas, Rhinomonas, Rhodomonas, Storeatula)

Haptista

Centroheliozoa

Centrohelea

Pterocystida

Choanocystidae Oxnerellidae Heterophryidae Pterocystidae

Acanthocystida

Marophryidae Raphidiophryidae Acanthocystidae

Haptophyta

Rappephyceae

Rappemonadales

Rappemonas

Pavlovophyceae

Pavlovales

Pavlovaceae

Prymnesiophyceae

Coccolithales (Pleurochrysis, Coccolithus) Prymnesiales (Chrysochromulina, Prymnesium) Isochrysidales
Isochrysidales
(Chrysotila, Dicrateria, Emiliania, Gephyrocapsa, Isochrysis) See also: coccolithophores

v t e

Eukaryota: SAR: Heterokonta
Heterokonta
or Stramenopiles

Domain Archaea Bacteria Eukaryota (Supergroup Plant Hacrobia Heterokont Alveolata Rhizaria Excavata Amoebozoa Opisthokonta

Animal Fungi)

Ochrophyta (mostly photosynthetic)

Phaeista

Hypogyristea

Pinguiophyceae Pelagophyceae

Dictyochophyceae/ Actinochrysophyceae/ Axodines

Dictyochales/Silicoflagellates Rhizochromulinales Florenciellales Actinodines

Pedinellales Ciliophryida Actinophryida

Chrysista

Chrysophyceae, golden algae

Chromulinales Chrysosphaerales Hibberdiales Hydrurales Phaeothamniales

Eustigmatophyceae

Eustigmataceae Monodopsidaceae Pseudocharaciopsidaceae

Phaeophyceae, brown algae

Ascoseirales Cutleriales Desmarestiales Dictyotales Discosporangiales Ectocarpales Fucales Ishigeales Laminariales Nemodermatales Onslowiales Ralfsiales Scytosiphonales Scytothamnales Sphacelariales Sporochnales Syringodermatales Tilopteridales

Phaeothamniophyceae

Phaeothamniales Pleurochloridellales

Raphidophyceae

Chattonella, Fibrocapsa, Gonyostomum, Haramonas, Heterosigma, Vacuolaria

Synurophyceae

Heterogloeales Ochromonadales Rhizochloridales Synurales

Xanthophyceae, yellow-green algae

Botrydiales Mischococcales Tribonematales Vaucheriales

Khakista

Bolidophyceae

Bolidomonas

Bacillariophyta, diatoms

Coscinodiscophyceae

Biddulphiophycidae Chaetocerotophycidae Corethrophycidae Coscinodiscophycidae Cymatosirophycidae Lithodesmiophycidae Rhizosoleniophycidae Thalassiosirophycidae

Bacillariophyceae

Bacillariales Naviculales

Fragilariophyceae

Fragilariales

Heterotrophic groups

Pseudofungi

Oomycetes Hyphochytriomycetes

Bigyra

Bigyromonadea Bicosoecea

Sagenista

Labyrinthulomycetes Eogyrea

Opalinata/Slopalinida

Opalinidae Proteromonadidae Blastocystis

v t e

Eukaryota: SAR: Alveolata

Domain Archaea Bacteria Eukaryota (Supergroup Plant Hacrobia Heterokont Alveolata Rhizaria Excavata Amoebozoa Opisthokonta

Animal Fungi)

Acavomonidia

Acavomonadea

Acavomonadida (Acavomonas)

Ciliophora

Intramacronucleata

Armophorea (Metopus) Cariacotrichea (Cariacothrix caudata) Colpodea
Colpodea
(Colpoda) Litostomatea
Litostomatea
(Balantidium, Dileptus) Nassophorea (Nassula) Oligohymenophorea
Oligohymenophorea
(Ichthyophthirius, Paramecium, Tetrahymena, Vorticella) Phyllopharyngea
Phyllopharyngea
(Chilodonella, Tokophrya) Plagiopylea (Plagiopyla) Prostomatea
Prostomatea
(Coleps, Holophrya) Protocruziea (Protocruzia) Spirotrichea (Euplotes, Stylonychia)

Postciliodesmatophora

Heterotrichea (Stentor, Climacostomum, Blepharisma) Karyorelictea
Karyorelictea
(Loxodes, Tracheloraphis)

Mesodiniea (Mesodinium, Myrionecta)

Colponemidia

Colponemadea

Colponemadida (Colponema)

Myzozoa

Apicomplexa

Aconoidasida

Haemospororida

Garniidae (Garnia) Haemoproteidae
Haemoproteidae
(Haemoproteus) Leucocytozoidae (Leucocytozoon) Plasmodiidae
Plasmodiidae
(Plasmodium)

Piroplasmida

Babesiidae (Babesia) Theileriidae (Theileria)

Conoidasida

Coccidia

Agamococcidiorida

Gemmocystidae (Gemmocystis) Rhytidocystidae (Rhytidocystis)

Eucoccidiorida

Adeleorina

Adeleidae Dactylosomatidae
Dactylosomatidae
(Babesiosoma, Dactylosoma) Haemogregarinidae
Haemogregarinidae
(Haemogregarina) Hepatozoidae
Hepatozoidae
(Hepatozoon) Karyolysidae (Karyolysus) Klossiellidae
Klossiellidae
(Klossiella) Legerellidae
Legerellidae
(Legerella)

Eimeriorina

Aggregatidae (Aggregata, Grasseella, Merocystis, Ovivora, Pseudoklossia, Selysina) Atoxoplasmatidae Barrouxiidae Calyptosporiidae Caryotrophidae Cryptosporidiidae
Cryptosporidiidae
(Cryptosporidium) Eimeriidae
Eimeriidae
(Cyclospora, Eimeria, Isospora) Elleipsisomatidae Lankesterellidae Selenococcidiidae

Sarcocystidae

Sarcocystinae (Frenkelia, Sarcocystis) Toxoplasmatinae (Besnoitia, Hammondia, Hyaloklossia, Nephroisospora, Neospora, Toxoplasma)

Ixorheorida

Ixorheidae (Ixorheis)

Protococcidiorida

Angeiocystidae (Angeiocystis) Eleutheroschizonidae (Coelotropha, Defretinella, Eleutheroschizon) Grelliidae (Coelotropha, Grellia) Mackinnoniidae (Mackinnonia) Myriosporidae (Myriosporides, Myriospora)

Gregarinia

Archigregarinorida

Exoschizonidae (Exoschizon) Selenidioididae (Merogregarina, Meroselenidium, Selenidioides, Veloxidium)

Eugregarinorida

Aseptatorina

Aikinetocystidae Allantocystidae Diplocystidae Enterocystidae Ganymedidae Lecudinidae Monocystidae (Monocystinae, Oligochaetocystinae, Rhynchocystinae, Stomatophorinae, Zygocystinae) Schaudinnellidae Selenidiidae Thiriotiidae Urosporidae

Blastogregarinorina

Siedleckiidae (Siedleckia)

Septatorina

Fusionicae (Fusionidae) Gregarinicae (Cephaloidophoridae, Cephalolobidae, Didymophoridae, Gregarinidae, Hirmocystidae, Metameridae, Uradiophoridae) Porosporicae (Porosporidae) Stenophoricae (Acutidae, Amphiplatysporidae, Brustiophoridae, Cnemidosporidae, Dactylophoridae, Leidyanidae, Monoductidae, Monoicidae, Sphaerocystidae, Stenophoridae, Trichorhynchidae) Stylocephaloidea (Actinocephalidae, Stylocephalidae) Blabericolidae

Neogregarinorida

Schizogregarinina (Caulleryellidae, Ophryocystidae) Gigaductidae (Gigaductus) Lipotrophidae (Apicystis, Farinocystis, Lipotropha, Lipocystis, Mattesia, Menzbieria) Schizocystidae (Lymphotropha, Machadoella, Schizocystis) Syncystidae (Syncystis)

Apicomonadea

Chromerida

Chromeraceae (Chromera velia) Vitrellaceae (Vitrella brassicaformis)

Colpodellida

Colpodellidae (Colpodella)

Voromonadida

Alphamonadidae (Alphamonas) Voromonadidae (Voromonas)

Dinoflagellata

Dinokaryota

With a theca: Dinophysiales
Dinophysiales
(Dinophysis, Histioneis, Ornithocercus, Oxyphysis) Gonyaulacales (Ceratium, Gonyaulax) Peridiniales (Pfiesteria, Peridinium) Prorocentrales
Prorocentrales
(Prorocentrum)

Without theca: Gymnodiniales
Gymnodiniales
(Amphidinium, Gymnodinium, Karenia, Karlodinium) Suessiales (Polarella, Symbiodinium)

Noctilucea

Noctilucales
Noctilucales
(Noctiluca)

Syndinea

Syndiniales: Amoebophryaceae (Amoebophyra) Duboscquellaceae (Duboscquella) Syndiniaceae (Hematodinium, Syndinium)

Other

Acrocoelidae (Acrocoelus) Ichthyodinium Oxyrrhinaceae
Oxyrrhinaceae
(Oxyrrhis) Pronoctilucidae (Pronoctiluca) Psammosidae (Psammosa)

Perkinsozoa

Perkinsea

Perkinsidae (Perkinsus) Phagodinida (Phagodinium) Rastromonadida (Parvilucifera, Rastrimonas)

Protoalveolata

Ellobiopsea

Ellobiopsidae (Elliobiocystis, Ellobiopsis, Parallobiopsis, Thalassomyces, Rhizellobiopsis)

Myzomonadea

Algovorida

Algovoridae (Algovora)

Chilovorida

Chilovoridae (Chilovora)

Squirmidea

Squirmidae (Filipodium, Platyproteum)

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Amoebozoa

Domain Archaea Bacteria Eukaryota (Supergroup Plant Hacrobia Heterokont Alveolata Rhizaria Excavata Amoebozoa Opisthokonta

Animal Fungi)

Lobosa

Cutosea

Squamocutida

Squamamoebidae Sapocribridae

Glycopoda

Discosea

Hyalodiscida

Hyalodiscidae

Centramoebia

Centramoebida

Acanthamoebidae Balamuthiidae

Cochliopodiida

Parvamoebina

Parvamoebidae

Tectiferina

Cochliopodiidae

Pellitina

Pellitidae Goceviidae

Flabellinia

Thecamoebida

Stenamoebidae Thecamoebidae

Mayorellidae

Mayorella

Dermamoebida

Dermamoebidae

Glycostylida

Vannellina

Vannellidae Discamoebidae

Stygamoebina

Stygamoebidae

Dactylopodina

Paramoebidae Vexilliferidae

Tubulinea

Echinamoebida

Echinamoebidae Vermamoebidae

Leptomyxida

Flabellina

Flabellulidae

Leptomyxina

Gephyramoebidae Leptomyxidae

Neolobosia

Trichosida

Trichosphaerium

Eulobosia

Euamoebida

Nolandellidae Amoebidae Hartmannellidae

Arcellinida

Phryganellina Eulobosina

Centropyxidae Difflugidae

Conosa

Archamoebae

incertae sedis

Tricholimacidae Endamoebidae

Entamoebida

Entamoebidae

Pelobiontida

Pelomyxina

Pelomyxidae

Mastigamoebina

Mastigamoebidae

Semiconosia

Variosea (paraphyletic)

Holomastigida Phalansteriida Artodiscida Varipodida

Mycetozoa

Myxogastria

Echinosteliopsida Ceratiomyxida Lucisporidia

Liceida Trichiida

Echinostelida

Echinosteliidae Clastodermidae

Fuscisporida

Lamprodermina Stemonitina Physarina

Others

Protosteliales Protosporangiida Dictyosteliida

Incertae sedis

Multicilia

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Opisthokonta

Domain Archaea Bacteria Eukaryota (Supergroup Plant Hacrobia Heterokont Alveolata Rhizaria Excavata Amoebozoa Opisthokonta

Animal Fungi)

Holomycota

Cristidiscoidea

Nucleariida

Nucleariidae

Fonticulida

Fonticulaceae

O+F

Opisthosporidia

Aphelida

Aphelidea

Aphelidida

C+M

Cryptomycota

Rozellidea

Rozellida

Microsporidia

Metchnikovellea

Metchnikovellida

Microsporea

Chytridiopsida Glugeida Meiodihaplophasida Dissociodihaplophasida

True Fungi

Neocallimastigomycota Chytridiomycota Blastocladiomycota Olpidiomycota Entomophthoromycota Kickxellomycota Mucoromycota Glomeromycota Entorrhizomycota Ascomycota Basidiomycota

Holozoa

Ichthyosporea

Dermocystida

Rhinosporidiaceae

Ichthyophonida

Sphaeroformina

Psorospermidae Piridae Creolimacidae

Trichomycina

Ichthyophonidae Amoebidiidae Palavasciaceae Parataeniellaceae Eccrinaceae

P+F

Pluriformea

Corallochytrea

Corallochytriida

Corallochytriidae

Syssomonas multiformis

Filozoa

Filasterea

Ministeriida

Capsasporidae Ministeriidae

Apoikozoa

Choanoflagellate

Acanthoecida

Stephanoecidae Acanthoecidae

Craspedida

Codonosigidae Salpingoecidae

Metazoa (Animalia)

Porifera Ctenophora Placozoa Cnidaria Xenacoelomorpha Deuterostome

chordates echinoderms

Protostome

Ecdysozoa
Ecdysozoa
inc. arthropods and nematodes Spiralia
Spiralia
inc. molluscs and annelids

Sources and alternative views: Wikispecies.

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Extant Animal
Animal
phyla

Domain Archaea Bacteria Eukaryota (Supergroup Plant Hacrobia Heterokont Alveolata Rhizaria Excavata Amoebozoa Opisthokonta

Animal Fungi)

A n i m a l i a

Porifera
Porifera
(sponges)

Diploblasts (Eumetazoa)

Ctenophora
Ctenophora
(comb jellies)

ParaHoxozoa

Placozoa
Placozoa
(Trichoplax)

Planulozoa

Cnidaria
Cnidaria
(jellyfish and relatives)

Bilateria (Triploblasts)

(see below↓)

Bilateria

Xenacoelomorpha

Xenoturbellida (Xenoturbella) Acoelomorpha

acoels nemertodermatids

N e p h r o z o a

Deuterostomia

Chordata

lancelets tunicates craniates / vertebrates

Ambulacraria

Echinodermata (starfish and relatives) Hemichordata

acorn worms pterobranchs

P r o t o s t o m i a

Ecdysozoa

Scalidophora

Kinorhyncha
Kinorhyncha
(mud dragons) Priapulida
Priapulida
(penis worms)

N+L+P

Nematoida

Nematoda (roundworms) Nematomorpha
Nematomorpha
(horsehair worms)

L+P

Loricifera

Panarthropoda

Arthropoda (arthropods) Tardigrada (waterbears) Onychophora
Onychophora
(velvet worms)

S p i r a l i a

Gnathifera¹

Chaetognatha
Chaetognatha
(arrow worms) Gnathostomulida (jaw worms) Micrognathozoa (Limnognathia) Syndermata

Rotifera Acanthocephala

Platytrochozoa

R+M

Mesozoa

Orthonectida Dicyemida
Dicyemida
or Rhombozoa

Rouphozoa¹

Platyhelminthes (flatworms) Gastrotricha (hairybacks)

Lophotrochozoa

Cycliophora (Symbion) Mollusca
Mollusca
(molluscs)

A+N

Annelida (ringed worms) Nemertea
Nemertea
(ribbon worms)

Lophophorata

Bryozoa

Entoprocta
Entoprocta
or Kamptozoa Ectoprocta (moss animals)

Brachiozoa

Brachiopoda (lamp shells) Phoronida (horseshoe worms)

Major groups within phyla

Sponges

Calcareous Hexactinellid Demosponge Homoscleromorpha

Cnidarians

Anthozoa
Anthozoa
inc. corals Medusozoa
Medusozoa
inc. jellyfish Myxozoa

Vertebrates

Jawless fish Cartilaginous fish Bony fish Amphibians Reptiles/Birds Mammals

Echinoderms

Sea lilies Asterozoa
Asterozoa
inc. starfish Echinozoa

Nematodes

Chromadorea Enoplea Secernentea

Arthropods

Chelicerates/Arachnids Myriapods Crustaceans Hexapods/Insects

Platyhelminths

Turbellaria Trematoda Monogenea Cestoda

Bryozoans

Phylactolaemata Stenolaemata Gymnolaemata

Annelids

Polychaetes Clitellata Echiura

Molluscs

Gastropods Cephalopods Bivalves Chitons Tusk shells

Phyla with ≥5000 extant species bolded See also Diploblasts Monoblastozoa (nomen dubium)

¹Platyzoa

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Opisthokont: True fungi classification, fungal orders

Domain Archaea Bacteria Eukaryota (Supergroup Plant Hacrobia Heterokont Alveolata Rhizaria Excavata Amoebozoa Opisthokonta

Animal Fungi)

Dikarya

Ascomycota (sac fungi)

Pezizomycotina

Leotiomyceta

Dothideomyceta

Coniocybomycetes Lichinomycetes Arthoniomycetes Dothideomycetes Eurotiomycetes Lecanoromycetes

Sordariomyceta

Xylonomycetes Geoglossomycetes Leotiomycetes Laboulbeniomycetes Sordariomycetes

Other

Orbiliomycetes Pezizomycetes

Saccharomycotina

Saccharomycetes

Taphrinomycotina

Archaeorhizomycetes Neolectomycetes Pneumocystidomycetes Schizosaccharomycetes Taphrinomycetes

Basidiomycota (with basidia)

Pucciniomycotina

Tritirachiomycetes Mixiomycetes Agaricostilbomycetes Cystobasidiomycetes Microbotryomycetes Classiculomycetes Cryptomycocolacomycetes Atractiellomycetes Pucciniomycetes

Ustilaginomycotina

Monilielliomycetes Malasseziomycetes Ustilaginomycetes Exobasidiomycetes

Agaricomycotina

Hymenomycete

Dacrymycetales Agaricomycetes

Other

Wallemiomycetes Bartheletiomycetes Tremellomycetes

Entorrhizomycota

Entorrhizomycetes

Glomeromycota

Glomeromycetes

Zygomycota (paraphyletic)

Mucoromycotina

Mortierellomycetes Mucoromycetes

Kickxellomycotina

Zoopagomycetes Kickxellomycetes

Entomophthoromycotina

Neozygitomycetes Basidiobolomycetes Entomophthoromycetes

Zoosporic fungi (paraphyletic)

Olpidiomycota

Olpidiomycetes

Blastocladiomycota

Blastocladiomycetes

Chytridiomycota

Neocallimastigomycetes Hyaloraphidiomycetes Monoblepharidomycetes Chytridiomycetes

Fungal phyla are underlined. See also: fungi imperfecti (polyphyletic group).

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Organisms and comparable organic structures

Life

Bacteria Archaea Eukaryota
Eukaryota
(Animalia Fungi Plantae Protista)

Non-cellular agents

Virus

ds DNA
DNA
virus ss DNA
DNA
virus dsRNA virus (+)ssRNA virus (−)ssRNA virus ssRNA-RT virus dsDNA-RT virus

Viroid

Pospiviroidae Avsunviroidae

Prion

Mammalian prion Fungal prion

Virus dependent

Satellite

ssRNA satellite virus ds DNA
DNA
satellite virus (Virophage) ss DNA
DNA
satellite dsRNA satellite ssRNA satellite (Virusoid)

Defective interfering particle

Defective Interfering RNA Defective interfering DNA

Taxon identifiers

Wd: Q19088 AlgaeBase: Lbeea6fab8cc1d7f8 EoL: 2908256 Fossilworks: 306691 NCBI: 2759

Authority control

.