37-469: The Stramenopiles , also called Heterokonts , are a clade of organisms distinguished by the presence of stiff tripartite external hairs. In most species, the hairs are attached to flagella , in some they are attached to other areas of the cellular surface, and in some they have been secondarily lost (in which case relatedness to stramenopile ancestors is evident from other shared cytological features or from genetic similarity). Stramenopiles represent one of
74-717: A phylogenetic tree . In the taxonomical literature, sometimes the Latin form cladus (plural cladi ) is used rather than the English form. Clades are the fundamental unit of cladistics , a modern approach to taxonomy adopted by most biological fields. The common ancestor may be an individual, a population , or a species ( extinct or extant ). Clades are nested, one in another, as each branch in turn splits into smaller branches. These splits reflect evolutionary history as populations diverged and evolved independently. Clades are termed monophyletic (Greek: "one clan") groups. Over
111-713: A polyphyletic grouping of various protists that have independently evolved axopodial arms. Some of the heliozoan groups are intermingled in the supergroup Rhizaria with radiolarians , their mostly marine counterpart. Actinophryida [REDACTED] Pedinellales [REDACTED] Phaeodaria [REDACTED] (classical radiolarians) Desmothoracida [REDACTED] Gymnosphaerida Acantharea [REDACTED] (classical radiolarians) Taxopodida Polycystinea [REDACTED] (classical radiolarians) Centroplasthelida [REDACTED] Microhelida [REDACTED] Plants Nucleariida [REDACTED] This eukaryote -related article
148-479: A "ladder", with supposedly more "advanced" organisms at the top. Taxonomists have increasingly worked to make the taxonomic system reflect evolution. When it comes to naming , this principle is not always compatible with the traditional rank-based nomenclature (in which only taxa associated with a rank can be named) because not enough ranks exist to name a long series of nested clades. For these and other reasons, phylogenetic nomenclature has been developed; it
185-623: A clade can be described based on two different reference points, crown age and stem age. The crown age of a clade refers to the age of the most recent common ancestor of all of the species in the clade. The stem age of a clade refers to the time that the ancestral lineage of the clade diverged from its sister clade. A clade's stem age is either the same as or older than its crown age. Ages of clades cannot be directly observed. They are inferred, either from stratigraphy of fossils , or from molecular clock estimates. Viruses , and particularly RNA viruses form clades. These are useful in tracking
222-553: A formal taxon Heliozoa or Heliozoea, with the rank of class or phylum, but it has been realised that they are polyphyletic , as the various orders show notable differences and are no longer believed to be descended from a single common ancestor. Instead, "heliozoa" is regarded as a descriptive term applying to various lines of protists. The primary groups include: Several nucleariids were once considered heliozoa, but they do not have microtubule-supported axopods and so are now considered filose amoeboids instead. The heliozoa are
259-550: A major role in recycling carbon and nutrients within microbial food webs . Stramenopiles are most closely related to Alveolates and Rhizaria, all of which have tubular mitochondrial cristae and collectively form the SAR supergroup , whose name is formed from their initials. The ancestor of the SAR supergroup appears to have captured a unicellular photosynthetic red alga , and many Stramenopiles, as well as members of other SAR groups such as
296-422: A revised taxonomy based on a concept strongly resembling clades, although the term clade itself would not be coined until 1957 by his grandson, Julian Huxley . German biologist Emil Hans Willi Hennig (1913–1976) is considered to be the founder of cladistics . He proposed a classification system that represented repeated branchings of the family tree, as opposed to the previous systems, which put organisms on
333-429: A suffix added should be e.g. "dracohortian". A clade is by definition monophyletic , meaning that it contains one ancestor which can be an organism, a population, or a species and all its descendants. The ancestor can be known or unknown; any and all members of a clade can be extant or extinct. The science that tries to reconstruct phylogenetic trees and thus discover clades is called phylogenetics or cladistics ,
370-499: Is also used with a similar meaning in other fields besides biology, such as historical linguistics ; see Cladistics § In disciplines other than biology . The term "clade" was coined in 1957 by the biologist Julian Huxley to refer to the result of cladogenesis , the evolutionary splitting of a parent species into two distinct species, a concept Huxley borrowed from Bernhard Rensch . Many commonly named groups – rodents and insects , for example – are clades because, in each case,
407-601: Is consistently recovered as the sister clade to all other stramenopiles. In addition, a flagellate species discovered in 2023, Kaonashia insperata , remains in an uncertain phylogenetic position, but more closely related to Gyrista than to other clades. Platysulcus Labyrinthulomycetes [REDACTED] Eogyrea Placididea Nanomonadea Opalinata [REDACTED] Bicosoecida [REDACTED] Developea Pirsonea Hyphochytriomycetes Oomycetes [REDACTED] Ochrophyta (=Heterokontophyta) [REDACTED] Kaonashia The classification of
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#1732780543254444-476: Is in turn included in the mammal, vertebrate and animal clades. The idea of a clade did not exist in pre- Darwinian Linnaean taxonomy , which was based by necessity only on internal or external morphological similarities between organisms. Many of the better known animal groups in Linnaeus's original Systema Naturae (mostly vertebrate groups) do represent clades. The phenomenon of convergent evolution
481-515: Is responsible for many cases of misleading similarities in the morphology of groups that evolved from different lineages. With the increasing realization in the first half of the 19th century that species had changed and split through the ages, classification increasingly came to be seen as branches on the evolutionary tree of life . The publication of Darwin's theory of evolution in 1859 gave this view increasing weight. In 1876 Thomas Henry Huxley , an early advocate of evolutionary theory, proposed
518-489: Is still controversial. As an example, see the full current classification of Anas platyrhynchos (the mallard duck) with 40 clades from Eukaryota down by following this Wikispecies link and clicking on "Expand". The name of a clade is conventionally a plural, where the singular refers to each member individually. A unique exception is the reptile clade Dracohors , which was made by haplology from Latin "draco" and "cohors", i.e. "the dragon cohort "; its form with
555-421: Is without such embellishments, being smooth, usually shorter, or in a few cases not projecting from the cell. The term 'heterokont' is used both as an adjective – indicating that a cell has two dissimilar flagella, and as the name of a taxon. The groups included in that taxon have however varied widely, creating the 'heterokont problem', now resolved by the definition of the stramenopiles. The term 'stramenopile'
592-492: The Xanthophyceae . But the same term was used for other groupings of algae. For example, in 1956, Copeland used it to include the xanthophytes (using the name Vaucheriacea), a group that included what became known as the chrysophytes , the silicoflagellates , and the hyphochytrids . Copeland also included the unrelated collar flagellates (as the choanoflagellates ) in which he placed the bicosoecids . He also included
629-407: The amoeboid cell body, and are variously used for capturing food, sensation, movement, and attachment. They are similar to Radiolaria , but they are distinguished from them by lacking central capsules and other complex skeletal elements, although some produce simple scales and spines. They may be found in both freshwater and marine environments. Originally the heliozoa were treated together as
666-525: The axodine lineage that included the chromophytic pedinellids , colourless ciliophryids, and colourless actinophryid heliozoa) have secondarily reverted to heterotrophy. Some stramenopiles are significant as autotrophs and as heterotrophs in natural ecosystems; others are parasitic. Blastocystis is a gastrointestinal parasite of humans; opalines and proteromonads live in the intestines of cold-blooded vertebrates and have been described as parasitic; oomycetes include some significant plant pathogens such as
703-465: The brown algae (wracks and many other seaweeds), and the diatoms . The latter are among the most significant primary producers in marine and freshwater ecosystems. Most molecular analyses suggest that the most basal stramenopiles lacked plastids and were accordingly colourless heterotrophs , feeding on other organisms. This implies that the stramenopiles arose as heterotrophs, diversified, and then some of them acquired chromoplasts. Some lineages (such as
740-557: The Rhizaria, still have plastids which retain the double membrane of the red alga and a double membrane surrounding it, for a total of four membranes. In addition, species of Telonemia , the sister group to SAR, exhibit heterokont flagella with tripartite mastigonemes, implying a more ancient origin of stramenopile characteristics. Telonemia [REDACTED] Rhizaria [REDACTED] Stramenopiles [REDACTED] Alveolata [REDACTED] The following cladogram summarizes
777-468: The Stramenopiles according to Adl et al. (2019), with additions from newer research: Clade In biological phylogenetics , a clade (from Ancient Greek κλάδος (kládos) 'branch'), also known as a monophyletic group or natural group , is a grouping of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on
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#1732780543254814-491: The algae with chromoplasts (chlorophylls a and c) than had previously been recognized. At the same time, a protistological perspective was replacing the 19th century one based on the division of unicellular eukaryotes into animals and plants. One consequence was that an array of heterotrophic organisms, many not previously considered as 'heterokonts', were seen as related to the 'core heterokonts' (those having anterior flagella with stiff hairs). Newly recognized relatives included
851-445: The cause of potato blight, Phytophthora infestans . Diatoms are major contributors to global carbon cycles because they are the most important autotrophs in most marine habitats. The brown algae, including familiar seaweeds like wrack and kelp, are major autotrophs of the intertidal and subtidal marine habitats. Some of the bacterivorous stramenopiles, such as Cafeteria , are common and widespread consumers of bacteria, and thus play
888-417: The evolutionary relationships between Stramenopiles. The phylogenetic relationships of Bigyra vary greatly from one analysis to the next: it has been recovered as either monophyletic or paraphyletic . When paraphyletic, the branching order of the bigyran groups also varies: in some studies Sagenista is the most basal-branching clade, while in others Opalozoa is the most basal. Nonetheless, Platysulcea
925-437: The genes that code for the proteins of these hairs are exclusive to stramenopiles. The presumed apomorphy of tripartite flagellar hairs in stramenopiles is well characterized. The basal part of the hair is flexible and inserts into the cell membrane; the second part is dominated by a long stiff tube (the 'straw' or 'stramen'); and finally the tube is tipped by many delicate hairs called mastigonemes . The proteins that code for
962-546: The group consists of a common ancestor with all its descendant branches. Rodents, for example, are a branch of mammals that split off after the end of the period when the clade Dinosauria stopped being the dominant terrestrial vertebrates 66 million years ago. The original population and all its descendants are a clade. The rodent clade corresponds to the order Rodentia, and insects to the class Insecta. These clades include smaller clades, such as chipmunk or ant , each of which consists of even smaller clades. The clade "rodent"
999-411: The group have been lost in some of the included taxa – for example in most diatoms . Many stramenopiles are unicellular flagellates , and most others produce flagellated cells at some point in their lifecycles, for instance as gametes or zoospores . Most flagellated heterokonts have two flagella; the anterior flagellum has one or two rows of stiff hairs or mastigonemes , and the posterior flagellum
1036-408: The identity, nature, character and relatedness of the group. The term 'stramenopile' sought to identify a clade (monophyletic and holophyletic lineage) using the approach developed by transformed cladists of pointing to a defining innovative characteristic or apomorphy. Over time, the scope of application has changed, especially when in the 1970s ultrastructural studies revealed greater diversity among
1073-590: The last few decades, the cladistic approach has revolutionized biological classification and revealed surprising evolutionary relationships among organisms. Increasingly, taxonomists try to avoid naming taxa that are not clades; that is, taxa that are not monophyletic . Some of the relationships between organisms that the molecular biology arm of cladistics has revealed include that fungi are closer relatives to animals than they are to plants, archaea are now considered different from bacteria , and multicellular organisms may have evolved from archaea. The term "clade"
1110-518: The latter term coined by Ernst Mayr (1965), derived from "clade". The results of phylogenetic/cladistic analyses are tree-shaped diagrams called cladograms ; they, and all their branches, are phylogenetic hypotheses. Three methods of defining clades are featured in phylogenetic nomenclature : node-, stem-, and apomorphy-based (see Phylogenetic nomenclature§Phylogenetic definitions of clade names for detailed definitions). The relationship between clades can be described in several ways: The age of
1147-471: The mastigonemes appear to be exclusive to the stramenopile clade, and are present even in taxa (such as diatoms) that no longer have such hairs. Most stramenopiles have two flagella near the apex. They are usually supported by four microtubule roots in a distinctive pattern. There is a transitional helix inside the flagellum where the beating axoneme with its distinctive geometric pattern of nine peripheral couplets around two central microtubules changes into
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1184-421: The nine-triplet structure of the basal body. Many stramenopiles have plastids which enable them to photosynthesise , using light to make their own food . Those plastids are coloured off-green, orange, golden or brown because of the presence of chlorophyll a , chlorophyll c , and fucoxanthin . This form of plastid is called a stramenochrome or chromoplast . The most significant autotrophic stramenopiles are
1221-475: The not-closely related haptophytes . The consequence of associating multiple concepts to the taxon 'heterokont' is that the meaning of 'heterokont' can only be made clear by making reference to its usage: Heterokontae sensu Luther 1899; Heterokontae sensu Copeland 1956, etc. This contextual clarification is rare, such that when the taxon name is used, it is unclear how it should be understood. The term 'Heterokont' has lost its usefulness in critical discussions about
1258-522: The parasitic opalines , proteromonads , and actinophryid heliozoa . They joined other heterotrophic protists, such as bicosoecids , labyrinthulids , and oomycete fungi, that were included by some as heterokonts and excluded by others. Rather than continue to use a name whose meaning had changed over time and was hence ambiguous, the name 'stramenopile' was introduced to refer to the clade of protists that had tripartite stiff (usually flagellar) hairs and all their descendants. Molecular studies confirm that
1295-643: The spread of viral infections . HIV , for example, has clades called subtypes, which vary in geographical prevalence. HIV subtype (clade) B, for example is predominant in Europe, the Americas and Japan, whereas subtype A is more common in east Africa. Heliozoa Heliozoa , commonly known as sun-animalcules, are microbial eukaryotes ( protists ) with stiff arms ( axopodia ) radiating from their spherical bodies, which are responsible for their common name. The axopodia are microtubule-supported projections from
1332-481: The three major clades in the SAR supergroup , along with Alveolata and Rhizaria . Stramenopiles are eukaryotes ; most are single-celled, but some are multicellular including some large seaweeds, the brown algae . The group includes a variety of algal protists , heterotrophic flagellates, opalines and closely related proteromonad flagellates (all endobionts in other organisms); the actinophryid heliozoa , and oomycetes . The tripartite hairs characteristic of
1369-418: Was introduced by D. J. Patterson in 1989, defining a group that overlapped with the ambiguously defined heterokonts . The name "stramenopile" has been discussed by J. C. David. The term 'heterokont' is used as both an adjective – indicating that a cell has two dissimilar flagella – and as the name of a taxon. The taxon 'Heterokontae' was introduced in 1899 by Alexander Luther for algae that are now considered
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