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37-555: Chromista is a proposed but polyphyletic biological kingdom , refined from the Chromalveolata , consisting of single-celled and multicellular eukaryotic species that share similar features in their photosynthetic organelles ( plastids ). It includes all eukaryotes whose plastids contain chlorophyll c and are surrounded by four membranes. If the ancestor already possessed chloroplasts derived by endosymbiosis from red algae , all non-photosynthetic Chromista have secondarily lost

74-472: A and c , together with phycobiliproteins and other pigments, and vary in color (brown, red to blueish-green). Each is surrounded by four membranes, and there is a reduced cell nucleus called a nucleomorph between the middle two. This indicates that the plastid was derived from a eukaryotic symbiont, shown by genetic studies to have been a red alga . However, the plastids are very different from red algal plastids: phycobiliproteins are present but only in

111-453: A node-based clade definition , for example, could be "All descendants of the last common ancestor of species X and Y". On the other hand, polyphyletic groups can be delimited as a conjunction of several clades, for example "the flying vertebrates consist of the bat, bird, and pterosaur clades". From a practical perspective, grouping species monophyletically facilitates prediction far more than does polyphyletic grouping. For example, classifying

148-492: A periplast , ejectisomes with secondary scroll, and mitochondrial cristae with flat tubules. Genetic studies as early as 1994 also supported the hypothesis that Goniomonas was sister to Cryptophyceae. A study in 2018 found strong evidence that the common ancestor of Cryptomonada was an autotrophic protist. Cryptomonads are distinguished by the presence of characteristic extrusomes called ejectosomes , which consist of two connected spiral ribbons held under tension. If

185-572: A common ancestor. This is thought to have occurred repeatedly, so that the red plastids spread from one group to another. The plastids, far from characterising their hosts as belonging to a single clade, thus have a different history from their disparate hosts. They appear to have originated in the Rhodophytina , and to have been transmitted to the Cryptophytina and from them to both the Ochrophyta and

222-449: A common phenomenon in nature, particularly in plants where polyploidy allows for rapid speciation. Some cladist authors do not consider species to possess the property of "-phyly", which they assert applies only to groups of species. Cryptophyta The cryptomonads (or cryptophytes ) are a group of algae , most of which have plastids . They are traditionally considered a division of algae among phycologists , under

259-430: A four-membrane envelope, as a result of which they acquired many other membrane proteins for transporting molecules in and out of the organelles. The diversity of chromists is hypothesised to have arisen from degeneration, loss or replacement of the plastids in some lineages. Additional symbiogenesis of green algae has provided genes retained in some members (such as heterokonts), and bacterial chlorophyll (indicated by

296-409: A new kingdom, saying: I established Chromista as a kingdom distinct from Plantae and Protozoa because of the evidence that chromist chloroplasts were acquired secondarily by enslavement of a red alga, itself a member of kingdom Plantae, and their unique membrane topology. Since then Chromista has been defined in different ways at different times. In 2010, Cavalier-Smith reorganised Chromista to include

333-421: A newly discovered grass in the monophyletic family Poaceae , the true grasses, immediately results in numerous predictions about its structure and its developmental and reproductive characteristics, that are synapomorphies of this family. In contrast, Linnaeus' assignment of plants with two stamens to the polyphyletic class Diandria, while practical for identification, turns out to be useless for prediction, since

370-490: A separate algae group, class Cryptophyceae or division Cryptophyta, while zoologists treated them as the flagellate protozoa order Cryptomonadina. In some classifications, the cryptomonads were considered close relatives of the dinoflagellates because of their (seemingly) similar pigmentation, being grouped as the Pyrrhophyta . Cryptomonad chloroplasts are closely related to those of the heterokonts and haptophytes , and

407-420: A single endosymbiotic event involving the ancestor of all chromists. The Chromalveolata included Stramenopiles , Haptophyta , Cryptophyta and Alveolata . However, in 2008 the group was found not to be monophyletic, and later studies confirmed this. In 2015, Cavalier-Smith and his colleagues made a new higher-level grouping of all organisms as a revision of the seven kingdoms model. In it, they classified

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444-546: Is different from the phylogeny of the host cells. In 2021, Jürgen Strassert and colleagues modelled the timelines for the presumed spread of the red plastids, concluding that "the hypotheses of serial endosymbiosis are chronologically possible, as the stem lineages of all red plastid-containing groups overlap in time" during the Mesoproterozoic and Neoproterozoic eras. They propose that the plastids were transmitted between groups as follows: Polyphyletic For example,

481-508: Is evidence that suggests the haptophytes and cryptomonads do not belong together with the heterokonts or the SAR clade, but may be associated with the Archaeplastida . Cryptista specifically may be sister or part of Archaeplastida, though this could be an artefact due to acquisition of genes from red algae by cryptomonads. A 2020 phylogeny of the eukaryotes states that "the chromalveolate hypothesis

518-459: Is not widely accepted" (noting Cavalier-Smith et al 2018 as an exception), explaining that the host lineages do not appear to be closely related in "most phylogenetic analyses". Further, none of TSAR, Cryptista, and Haptista, groups formerly within Chromalveolata, appear "likely to be ancestrally defined by red secondary plastids". This is because of the many non-photosynthetic organisms related to

555-583: Is often the stimulus for major revisions of the classification schemes. Researchers concerned more with ecology than with systematics may take polyphyletic groups as legitimate subject matter; the similarities in activity within the fungus group Alternaria , for example, can lead researchers to regard the group as a valid genus while acknowledging its polyphyly. In recent research, the concepts of monophyly, paraphyly, and polyphyly have been used in deducing key genes for barcoding of diverse groups of species. The term polyphyly , or polyphyletic , derives from

592-670: The Haptophyta , and then from these last to the Myzozoa . Members of Chromista are single-celled and multicellular eukaryotes having basically either or both features: The kingdom includes diverse organisms from algae to malarial parasites ( Plasmodium ). Molecular evidence indicates that the plastids in chromists were derived from red algae through secondary symbiogenesis in a single event. In contrast, plants acquired their plastids from cyanobacteria through primary symbiogenesis . These plastids are now enclosed in two extra cell membranes, making

629-694: The SAR supergroup (named for the included groups Stramenopiles , Alveolata and Rhizaria ) and Hacrobia ( Haptista and Cryptista ). Patron et al . (2004) considered the presence of a unique class of FBA (fructose-1,6-biophosphate-aldolase) enzyme not similar to that found in plants as evidence of chromist monophyly. Fast et al . (2001) supported a single origin for the myzozoan (dinoflagellate + apicomplexan), heterokont and cryptophyte plastids based on their comparison of GAPDH (glyceraldehyde-3-phosphate dehydrogenase) genes. Harper & Keeling (2003) described haptophyte homologs and considered them further evidence of

666-405: The endoplasmic reticulum and transported to the cell surface. Small scales may also be present on the flagella and cell body. The mitochondria have flat cristae , and mitosis is open; sexual reproduction has also been reported. The first mention of cryptomonads appears to have been made by Christian Gottfried Ehrenberg in 1831, while studying Infusoria . Later, botanists treated them as

703-528: The ability to photosynthesise. Its members might have arisen independently as separate evolutionary groups from the last eukaryotic common ancestor. Chromista as a taxon was created by the British biologist Thomas Cavalier-Smith in 1981 to distinguish the stramenopiles , haptophytes , and cryptophytes . According to Cavalier-Smith, the kingdom originally consisted mostly of photosynthetic eukaryotes ( algae ), but he later brought many heterotrophs ( protozoa ) into

740-406: The above phyla Cryptista and "N.N.", Haptista corresponds to the above phyla Haptophyta and Heliozoa): Cryptista Heliozoa Haptophyta Cercozoa Retaria Ciliophora Miozoa Bigyra Gyrista Molecular trees have had difficulty resolving relationships between the different groups. All three may share a common ancestor with the alveolates (see chromalveolates ), but there

777-444: The biological characteristic of warm-bloodedness evolved separately in the ancestors of mammals and the ancestors of birds; "warm-blooded animals" is therefore a polyphyletic grouping. Other examples of polyphyletic groups are algae , C4 photosynthetic plants , and edentates . Many taxonomists aim to avoid homoplasies in grouping taxa together, with a goal to identify and eliminate groups that are found to be polyphyletic. This

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814-578: The cells are irritated either by mechanical, chemical or light stress, they discharge, propelling the cell in a zig-zag course away from the disturbance. Large ejectosomes, visible under the light microscope, are associated with the pocket; smaller ones occur underneath the periplast , the cryptophyte-specific cell surrounding. Except for the class Goniomonadea , which lacks plastids entirely, and Cryptomonas paramecium (previously called Chilomonas paramecium ), which has leucoplasts , cryptomonads have one or two chloroplasts. These contain chlorophylls

851-417: The common ancestor of all eukaryotes: The four phyla that contain chromophyte algae (those with chlorophyll c--i.e., Cryptista, Heterokonta, Haptophyta, Dinozoa) are distantly related to each other and to Chlorarachniophyta on our trees. However, all of the photosynthetic taxa within each of these four phyla radiate from each other very substantially after the radiation of the four phyla themselves. This favors

888-529: The current Ochrophyta (autotrophic Stramenopiles ), Haptophyta , Cryptophyta , Dinophyta and Choanoflagellida . The Euglenophyceae were transferred to the Chlorophyta . The Chromophyta (Bourrelly, 1968) included the current Ochrophyta (autotrophic Stramenopiles ), Haptophyta and Choanoflagellida . The Cryptophyceae and the Dinophyceae were part of Pyrrhophyta (= Dinophyta). The name Chromista

925-432: The fact that a monophyletic group includes organisms consisting of all the descendants of a unique common ancestor. By comparison, the term paraphyly , or paraphyletic , uses the ancient Greek preposition παρά ( pará ) 'beside, near', and refers to the situation in which one or several monophyletic subgroups are left apart from all other descendants of a unique common ancestor. In many schools of taxonomy ,

962-400: The groups with chlorophyll c , and the possibility that cryptophytes are more closely related to plants. The alternative to monophyly is serial endosymbiosis , meaning that the "chromists" acquired their plastids from each other instead of inheriting them from a single common ancestor. Thus the phylogeny of the distinctive plastids, which are agreed to have a common origin in the rhodophytes,

999-453: The kingdom Chromista into 2 subkingdoms and 11 phyla, namely: Cryptista Heliozoa Haptophyta Endohelea Picomonadea Telonemea Cercozoa Retaria Ciliophora Miozoa Bigyra Pseudofungi (Oomycota) Ochrophyta Cavalier-Smith made a new analysis of Chromista in 2018 in which he classified all chromists into 8 phyla (Gyrista corresponds to the above phyla Ochrophyta and Pseudofungi, Cryptista corresponds to

1036-548: The name of Cryptophyta . They are common in freshwater, and also occur in marine and brackish habitats. Each cell is around 10–50 μm in size and flattened in shape, with an anterior groove or pocket. At the edge of the pocket there are typically two slightly unequal flagella . Some may exhibit mixotrophy . They are classified as clade Cryptomonada , which is divided into two classes: heterotrophic Goniomonadea and phototrophic Cryptophyceae . The two groups are united under three shared morphological characteristics: presence of

1073-400: The presence of exactly two stamens has developed convergently in many groups. Species have a special status in systematics as being an observable feature of nature itself and as the basic unit of classification. It is usually implicitly assumed that species are monophyletic (or at least paraphyletic ). However, hybrid speciation arguably leads to polyphyletic species. Hybrid species are

1110-736: The presence of ribosomal protein L36 gene, rpl36 ) in haptophytes and cryptophytes. Some examples of classification of the groups involved, which have overlapping but non-identical memberships, are shown below. The Chromophycées (Chadefaud, 1950), renamed Chromophycota (Chadefaud, 1960), included the current Ochrophyta (autotrophic Stramenopiles ), Haptophyta (included in Chrysophyceae until Christensen, 1962), Cryptophyta , Dinophyta , Euglenophyceae and Choanoflagellida (included in Chrysophyceae until Hibberd, 1975). The Chromophyta (Christensen 1962, 2008), defined as algae with chlorophyll c , included

1147-536: The proposed group. As of 2018, the kingdom was nearly as diverse as the kingdoms Plantae and Animalia, consisting of eight phyla. Notable members include marine algae, potato blight , dinoflagellates , Paramecium , the brain parasite Toxoplasma , and the malarial parasite Plasmodium . However, Cavalier-Smith's hypothesis of chromist monophyly has been rejected by other researchers, who consider it more likely that some chromists acquired their plastids by incorporating another chromist instead of inheriting them from

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1184-494: The recognition of polyphyletic groups in a classification is discouraged. Monophyletic groups (that is, clades ) are considered by these schools of thought to be the only valid groupings of organisms because they are diagnosed ("defined", in common parlance) on the basis of synapomorphies , while paraphyletic or polyphyletic groups are not. From the perspective of ancestry, clades are simple to define in purely phylogenetic terms without reference to clades previously introduced:

1221-527: The three groups were united by Cavalier-Smith as the Chromista . However, the case that the organisms themselves are closely related was counter-indicated by the major differences in cell organization ( ultrastructural identity ), suggesting that the three major lineages assigned to the chromists had acquired plastids independently, and that chromists are polyphyletic. The perspective that cryptomonads are primitively heterotrophic and secondarily acquired chloroplasts,

1258-700: The thylakoid lumen and are present only as phycoerythrin or phycocyanin . In the case of Rhodomonas , the crystal structure has been determined to 1.63   Å; and it has been shown that the alpha subunit bears no relation to any other known phycobiliprotein. A few cryptomonads, such as Cryptomonas , can form palmelloid stages, but readily escape the surrounding mucus to become free-living flagellates again. Some Cryptomonas species may also form immotile microbial cysts —resting stages with rigid cell walls to survive unfavorable conditions. Cryptomonad flagella are inserted parallel to one another, and are covered by bipartite hairs called mastigonemes , formed within

1295-405: The two Ancient Greek words πολύς ( polús ) 'many, a lot of', and φῦλον ( phûlon ) 'genus, species', and refers to the fact that a polyphyletic group includes organisms (e.g., genera, species) arising from multiple ancestral sources. Conversely, the term monophyly , or monophyletic , employs the ancient Greek adjective μόνος ( mónos ) 'alone, only, unique', and refers to

1332-432: The view that the common ancestor of these four phyla was not photosynthetic and that chloroplasts were implanted separately into each much more recently. This probable polyphyly of the chromophyte algae, if confirmed, would make it desirable to treat Cryptista, Heterokonta, and Haptophyta as separate kingdoms, rather than to group them together in the single kingdom Chromista. In 2009, Cavalier-Smith gave his reason for making

1369-503: Was first introduced by Cavalier-Smith in 1981; the earlier names Chromophyta, Chromobiota and Chromobionta correspond to roughly the same group. It has been described as consisting of three different groups: It includes all protists whose plastids contain chlorophyll c . In 1994, Cavalier-Smith and colleagues indicated that the Chromista is probably a polyphyletic group whose members arose independently, sharing no more than descent from

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