63-426: The Apicomplexa (also called Apicomplexia ; single: apicomplexan ) are organisms of a large phylum of mainly parasitic alveolates . Most possess a unique form of organelle structure that comprises a type of non-photosynthetic plastid called an apicoplast —with an apical complex membrane . The organelle's apical shape ( e.g., see Ceratium furca ) is an adaptation that the apicomplexan applies in penetrating
126-476: A phylum ( / ˈ f aɪ l əm / ; pl. : phyla ) is a level of classification or taxonomic rank below kingdom and above class . Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature for algae, fungi, and plants accepts the terms as equivalent. Depending on definitions, the animal kingdom Animalia contains about 31 phyla,
189-480: A biological basis, as the ability to store haemozoin appears to have evolved only once. Roberts and Janovy in 1996 divided the phylum into the following subclasses and suborders (omitting classes and orders): These form the following five taxonomic groups: Perkins et al. proposed the following scheme. It is outdated as the Perkinsidae have since been recognised as a sister group to the dinoflagellates rather that
252-551: A certain degree of morphological or developmental similarity (the phenetic definition), or a group of organisms with a certain degree of evolutionary relatedness (the phylogenetic definition). Attempting to define a level of the Linnean hierarchy without referring to (evolutionary) relatedness is unsatisfactory, but a phenetic definition is useful when addressing questions of a morphological nature—such as how successful different body plans were. The most important objective measure in
315-407: A character unique to a sub-set of the crown group. Furthermore, organisms in the stem group of a phylum can possess the "body plan" of the phylum without all the characteristics necessary to fall within it. This weakens the idea that each of the phyla represents a distinct body plan. A classification using this definition may be strongly affected by the chance survival of rare groups, which can make
378-539: A comprehensive survey of the phylum was completed: in all, 4516 species and 339 genera had been named. They consisted of: Although considerable revision of this phylum has been done (the order Haemosporidia now has 17 genera rather than 9), these numbers are probably still approximately correct. Jacques Euzéby in 1988 created a new class Haemosporidiasina by merging subclass Piroplasmasina and suborder Haemospororina . The division into Achromatorida and Chromatorida, although proposed on morphological grounds, may have
441-527: A diverse group that includes organisms such as the coccidia , gregarines , piroplasms , haemogregarines , and plasmodia . Diseases caused by Apicomplexa include: The name Apicomplexa derives from two Latin words— apex (top) and complexus (infolds)—for the set of organelles in the sporozoite . The Apicomplexa comprise the bulk of what used to be called the Sporozoa , a group of parasitic protozoans, in general without flagella, cilia, or pseudopods. Most of
504-408: A drug that harms an apicomplexan parasite is also likely to harm its human host. At present, no effective vaccines are available for most diseases caused by these parasites. Biomedical research on these parasites is challenging because it is often difficult, if not impossible, to maintain live parasite cultures in the laboratory and to genetically manipulate these organisms. In recent years, several of
567-402: A group ("a self-contained unity"): "perhaps such a real and completely self-contained unity is the aggregate of all species which have gradually evolved from one and the same common original form, as, for example, all vertebrates. We name this aggregate [a] Stamm [i.e., stock] ( Phylon )." In plant taxonomy , August W. Eichler (1883) classified plants into five groups named divisions,
630-596: A group containing Viridiplantae and the algal Rhodophyta and Glaucophyta divisions. The definition and classification of plants at the division level also varies from source to source, and has changed progressively in recent years. Thus some sources place horsetails in division Arthrophyta and ferns in division Monilophyta, while others place them both in Monilophyta, as shown below. The division Pinophyta may be used for all gymnosperms (i.e. including cycads, ginkgos and gnetophytes), or for conifers alone as below. Since
693-463: A host cell. The Apicomplexa are unicellular and spore-forming. Most are obligate endoparasites of animals, except Nephromyces , a symbiont in marine animals, originally classified as a chytrid fungus, and the Chromerida , some of which are photosynthetic partners of corals. Motile structures such as flagella or pseudopods are present only in certain gamete stages. The Apicomplexa are
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#1732858609764756-410: A lack of cilia, sexual reproduction, use of micropores for feeding, and the production of oocysts containing sporozoites as the infective form. Transposons appear to be rare in this phylum, but have been identified in the genera Ascogregarina and Eimeria . Most members have a complex lifecycle, involving both asexual and sexual reproduction. Typically, a host is infected via an active invasion by
819-442: A large number of gametes and the zygote gives rise to an oocyst, which is the infective stage. The majority are monoxenous (infect one host only), but a few are heteroxenous (lifecycle involves two or more hosts). The number of families in this later suborder is debated, with the number of families being between one and 20 depending on the authority and the number of genera being between 19 and 25. The first Apicomplexa protozoan
882-488: A mean diameter around 0.7 μm. Secretion of the dense-granule content takes place after parasite invasion and localization within the parasitophorous vacuole and persists for several minutes. Replication: Mobility: Apicomplexans have a unique gliding capability which enables them to cross through tissues and enter and leave their host cells. This gliding ability is made possible by the use of adhesions and small static myosin motors. Other features common to this phylum are
945-503: A member of the Apicomplexa, has been moved to a new phylum — Perkinsozoa . The gregarines are generally parasites of annelids , arthropods , and molluscs . They are often found in the guts of their hosts, but may invade the other tissues. In the typical gregarine lifecycle, a trophozoite develops within a host cell into a schizont. This then divides into a number of merozoites by schizogony . The merozoites are released by lysing
1008-505: A phylogenetic clade containing Aggregata octopiana Frenzel 1885 , Merocystis kathae Dakin, 1911 (both Aggregatidae, originally coccidians), Rhytidocystis sp. 1 and Rhytidocystis sp. 2 Janouškovec et al. 2019 ( Rhytidocystidae Levine, 1979 , originally coccidians, Agamococcidiorida ), and Margolisiella islandica Kristmundsson et al. 2011 (closely related to Rhytidocystidae). Marosporida infect marine invertebrates. Members of this clade retain plastid genomes and
1071-400: A phylum based on body plan has been proposed by paleontologists Graham Budd and Sören Jensen (as Haeckel had done a century earlier). The definition was posited because extinct organisms are hardest to classify: they can be offshoots that diverged from a phylum's line before the characters that define the modern phylum were all acquired. By Budd and Jensen's definition, a phylum is defined by
1134-471: A phylum much more diverse than it would be otherwise. Total numbers are estimates; figures from different authors vary wildly, not least because some are based on described species, some on extrapolations to numbers of undescribed species. For instance, around 25,000–27,000 species of nematodes have been described, while published estimates of the total number of nematode species include 10,000–20,000; 500,000; 10 million; and 100 million. The kingdom Plantae
1197-689: A phylum, other phylum-level ranks appear, such as the case of Bacillariophyta (diatoms) within Ochrophyta . These differences became irrelevant after the adoption of a cladistic approach by the ISP, where taxonomic ranks are excluded from the classifications after being considered superfluous and unstable. Many authors prefer this usage, which lead to the Chromista-Protozoa scheme becoming obsolete. Currently there are 40 bacterial phyla (not including " Cyanobacteria ") that have been validly published according to
1260-412: A secretory body (the rhoptry ) and one or more polar rings. Additional slender electron-dense secretory bodies ( micronemes ) surrounded by one or two polar rings may also be present. This structure gives the phylum its name. A further group of spherical organelles is distributed throughout the cell rather than being localized at the apical complex and are known as the dense granules. These typically have
1323-401: A set of characters shared by all its living representatives. This approach brings some small problems—for instance, ancestral characters common to most members of a phylum may have been lost by some members. Also, this definition is based on an arbitrary point of time: the present. However, as it is character based, it is easy to apply to the fossil record. A greater problem is that it relies on
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#17328586097641386-522: A sister taxon to the Hematozoa. This genus is found in the renal sac of molgulid ascidian tunicates . Members of this phylum, except for the photosynthetic chromerids, are parasitic and evolved from a free-living ancestor. This lifestyle is presumed to have evolved at the time of the divergence of dinoflagellates and apicomplexans. Further evolution of this phylum has been estimated to have occurred about 800 million years ago . The oldest extant clade
1449-401: A subjective decision about which groups of organisms should be considered as phyla. The approach is useful because it makes it easy to classify extinct organisms as " stem groups " to the phyla with which they bear the most resemblance, based only on the taxonomically important similarities. However, proving that a fossil belongs to the crown group of a phylum is difficult, as it must display
1512-667: A subset. The phylum Apicomplexa contains all eukaryotes with a group of structures and organelles collectively termed the apical complex. This complex consists of structural components and secretory organelles required for invasion of host cells during the parasitic stages of the Apicomplexan life cycle . Apicomplexa have complex life cycles, involving several stages and typically undergoing both asexual and sexual replication . All Apicomplexa are obligate parasites for some portion of their life cycle, with some parasitizing two separate hosts for their asexual and sexual stages. Besides
1575-424: A term that remains in use today for groups of plants, algae and fungi. The definitions of zoological phyla have changed from their origins in the six Linnaean classes and the four embranchements of Georges Cuvier . Informally, phyla can be thought of as groupings of organisms based on general specialization of body plan . At its most basic, a phylum can be defined in two ways: as a group of organisms with
1638-437: A zygote that in its turn forms an oocyst that is normally released from the body. Syzygy, when it occurs, involves markedly anisogamous gametes. The lifecycle is typically haploid, with the only diploid stage occurring in the zygote, which is normally short-lived. The main difference between the coccidians and the gregarines is in the gamonts. In the coccidia, these are small, intracellular, and without epimerites or mucrons . In
1701-467: Is a paraphyletic taxon, which is less acceptable to present-day biologists than in the past. Proposals have been made to divide it among several new kingdoms, such as Protozoa and Chromista in the Cavalier-Smith system . Protist taxonomy has long been unstable, with different approaches and definitions resulting in many competing classification schemes. Many of the phyla listed below are used by
1764-405: Is defined in various ways by different biologists (see Current definitions of Plantae ). All definitions include the living embryophytes (land plants), to which may be added the two green algae divisions, Chlorophyta and Charophyta , to form the clade Viridiplantae . The table below follows the influential (though contentious) Cavalier-Smith system in equating "Plantae" with Archaeplastida ,
1827-472: Is generally included in kingdom Fungi, though its exact relations remain uncertain, and it is considered a protozoan by the International Society of Protistologists (see Protista , below). Molecular analysis of Zygomycota has found it to be polyphyletic (its members do not share an immediate ancestor), which is considered undesirable by many biologists. Accordingly, there is a proposal to abolish
1890-469: Is no longer regarded as biologically valid and its use is discouraged, although some authors still use it as a synonym for the Apicomplexa. More recently, other groups were excluded from Apicomplexa, e.g., Perkinsus and Colpodella (now in Protalveolata). The field of classifying Apicomplexa is in flux and classification has changed throughout the years since it was formally named in 1970. By 1987,
1953-429: Is the plastid, and in fact existing drugs such as tetracyclines , which are effective against apicomplexans, seem to operate against the plastid. Many Coccidiomorpha have an intermediate host , as well as a primary host, and the evolution of hosts proceeded in different ways and at different times in these groups. For some coccidiomorphs, the original host has become the intermediate host, whereas in others it has become
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2016-609: Is thought to be the archigregarines. These phylogenetic relations have rarely been studied at the subclass level. The Haemosporidia are related to the gregarines, and the piroplasms and coccidians are sister groups. The Haemosporidia and the Piroplasma appear to be sister clades, and are more closely related to the coccidians than to the gregarines. Marosporida is a sister group to Coccidiomorphea. Squirmida ( Digyalum , Filipodium , Platyproteum ) Chromerida ( Chromera , Vitrella , Piridium ) Phylum In biology ,
2079-629: The Bacteriological Code Currently there are 2 phyla that have been validly published according to the Bacteriological Code Other phyla that have been proposed, but not validly named, include: Microneme Micronemes are secretory organelles , possessed by parasitic apicomplexans . Micronemes are located on the apical third of the protozoan body. They are surrounded by a typical unit membrane . On electron microscopy they have an electron-dense matrix due to
2142-552: The Catalogue of Life , and correspond to the Protozoa-Chromista scheme, with updates from the latest (2022) publication by Cavalier-Smith . Other phyla are used commonly by other authors, and are adapted from the system used by the International Society of Protistologists (ISP). Some of the descriptions are based on the 2019 revision of eukaryotes by the ISP. The number of protist phyla varies greatly from one classification to
2205-402: The apicoplast which maintains a separate 35 kilobase circular genome (with the exception of Cryptosporidium species and Gregarina niphandrodes which lack an apicoplast). All members of this phylum have an infectious stage—the sporozoite—which possesses three distinct structures in an apical complex. The apical complex consists of a set of spirally arranged microtubules (the conoid ),
2268-626: The apicoplast , surrounded by either three or four membranes. Its functions are thought to include tasks such as lipid and heme biosynthesis, and it appears to be necessary for survival. In general, plastids are considered to have a common origin with the chloroplasts of dinoflagellates, and evidence points to an origin from red algae rather than green . Within this phylum are four groups — coccidians, gregarines, haemosporidians (or haematozoans, including in addition piroplasms), and marosporidians. The coccidians and haematozoans appear to be relatively closely related. Perkinsus , while once considered
2331-440: The epithelial cells of the gut, but may infect other tissues. The coccidian lifecycle involves merogony, gametogony, and sporogony. While similar to that of the gregarines it differs in zygote formation. Some trophozoites enlarge and become macrogamete , whereas others divide repeatedly to form microgametes (anisogamy). The microgametes are motile and must reach the macrogamete to fertilize it. The fertilized macrogamete forms
2394-457: The sporozoites . The sporozoites escape from the oocyst and migrate within the body of the vector to the salivary glands where they are injected into the new vertebrate host when the insect vector feeds again. The class Marosporida Mathur, Kristmundsson, Gestal, Freeman, and Keeling 2020 is a newly recognized lineage of apicomplexans that is sister to the Coccidia and Hematozoa. It is defined as
2457-422: The Apicomplexa among a group called the alveolates . Several related flagellates, such as Perkinsus and Colpodella , have structures similar to the polar ring and were formerly included here, but most appear to be closer relatives of the dinoflagellates . They are probably similar to the common ancestor of the two groups. Another similarity is that many apicomplexan cells contain a single plastid , called
2520-562: The Apicomplexa are motile, however, with a gliding mechanism that uses adhesions and small static myosin motors. The other main lines of this obsolete grouping were the Ascetosporea (a group of Rhizaria ), the Myxozoa (highly derived cnidarian animals ), and the Microsporidia (derived from fungi ). Sometimes, the name Sporozoa is taken as a synonym for the Apicomplexa, or occasionally as
2583-527: The Apicomplexia: The name Protospiromonadida has been proposed for the common ancestor of the Gregarinomorpha and Coccidiomorpha. Another group of organisms that belong in this taxon are the corallicolids. These are found in coral reef gastric cavities. Their relationship to the others in this phylum has yet to be established. Another genus has been identified - Nephromyces - which appears to be
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2646-491: The Zygomycota phylum. Its members would be divided between phylum Glomeromycota and four new subphyla incertae sedis (of uncertain placement): Entomophthoromycotina , Kickxellomycotina , Mucoromycotina , and Zoopagomycotina . Kingdom Protista (or Protoctista) is included in the traditional five- or six-kingdom model, where it can be defined as containing all eukaryotes that are not plants, animals, or fungi. Protista
2709-458: The above definitions is the "certain degree" that defines how different organisms need to be members of different phyla. The minimal requirement is that all organisms in a phylum should be clearly more closely related to one another than to any other group. Even this is problematic because the requirement depends on knowledge of organisms' relationships: as more data become available, particularly from molecular studies, we are better able to determine
2772-519: The anterior of the cell. These secrete enzymes that allow the parasite to enter other cells. The tip is surrounded by a band of microtubules , called the polar ring, and among the Conoidasida is also a funnel of tubulin proteins called the conoid. Over the rest of the cell, except for a diminished mouth called the micropore, the membrane is supported by vesicles called alveoli, forming a semirigid pellicle. The presence of alveoli and other traits place
2835-580: The apicomplexan species have been selected for genome sequencing . The availability of genome sequences provides a new opportunity for scientists to learn more about the evolution and biochemical capacity of these parasites. The predominant source of this genomic information is the EuPathDB family of websites, which currently provides specialised services for Plasmodium species ( PlasmoDB ), coccidians (ToxoDB), piroplasms (PiroplasmaDB), and Cryptosporidium species (CryptoDB). One possible target for drugs
2898-535: The canonical apicomplexan plastid metabolism. However, marosporidians have the most reduced apicoplast genomes sequenced to date, lack canonical plastidial RNA polymerase and so provide new insights into reductive organelle evolution. Many of the apicomplexan parasites are important pathogens of humans and domestic animals. In contrast to bacterial pathogens, these apicomplexan parasites are eukaryotic and share many metabolic pathways with their animal hosts. This makes therapeutic target development extremely difficult –
2961-443: The conserved apical complex, Apicomplexa are morphologically diverse. Different organisms within Apicomplexa, as well as different life stages for a given apicomplexan, can vary substantially in size, shape, and subcellular structure. Like other eukaryotes, Apicomplexa have a nucleus , endoplasmic reticulum and Golgi complex . Apicomplexa generally have a single mitochondrion, as well as another endosymbiont-derived organelle called
3024-466: The definitive host. In the genera Aggregata , Atoxoplasma , Cystoisospora , Schellackia , and Toxoplasma , the original is now definitive, whereas in Akiba , Babesiosoma , Babesia , Haemogregarina , Haemoproteus , Hepatozoon , Karyolysus , Leucocytozoon , Plasmodium , Sarcocystis , and Theileria , the original hosts are now intermediate. Similar strategies to increase
3087-504: The first publication of the APG system in 1998, which proposed a classification of angiosperms up to the level of orders , many sources have preferred to treat ranks higher than orders as informal clades. Where formal ranks have been provided, the traditional divisions listed below have been reduced to a very much lower level, e.g. subclasses . Wolf plants Hepatophyta Liver plants Coniferophyta Cone-bearing plant Phylum Microsporidia
3150-475: The gregarines, these are large, extracellular, and possess epimerites or mucrons. A second difference between the coccidia and the gregarines also lies in the gamonts. In the coccidians, a single gamont becomes a macrogametocyte, whereas in the gregarines, the gamonts give rise to multiple gametocytes. The Haemosporidia have more complex lifecycles that alternate between an arthropod and a vertebrate host. The trophozoite parasitises erythrocytes or other tissues in
3213-513: The high protein content. They are specialized secretory organelles important for host-cell invasion and gliding motility . These organelles secrete several proteins such as the Plasmodium falciparum apical membrane antigen-1 , or PfAMA1, and Erythrocyte family antigen, or EBA, family proteins. These proteins specialize in binding to erythrocyte surface receptors and facilitating erythrocyte entry. Only by this initial chemical exchange can
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#17328586097643276-441: The host cell, which in turn invade other cells. At some point in the apicomplexan lifecycle, gametocytes are formed. These are released by lysis of the host cells, which group together. Each gametocyte forms multiple gametes . The gametes fuse with another to form oocysts . The oocysts leave the host to be taken up by a new host. In general, coccidians are parasites of vertebrates . Like gregarines, they are commonly parasites of
3339-510: The likelihood of transmission have evolved in multiple genera. Polyenergid oocysts and tissue cysts are found in representatives of the orders Protococcidiorida and Eimeriida . Hypnozoites are found in Karyolysus lacerate and most species of Plasmodium ; transovarial transmission of parasites occurs in lifecycles of Karyolysus and Babesia . Horizontal gene transfer appears to have occurred early on in this phylum's evolution with
3402-411: The next. The Catalogue of Life includes Rhodophyta and Glaucophyta in kingdom Plantae, but other systems consider these phyla part of Protista. In addition, less popular classification schemes unite Ochrophyta and Pseudofungi under one phylum, Gyrista , and all alveolates except ciliates in one phylum Myzozoa , later lowered in rank and included in a paraphyletic phylum Miozoa . Even within
3465-528: The other hand, the highly parasitic phylum Mesozoa was divided into two phyla ( Orthonectida and Rhombozoa ) when it was discovered the Orthonectida are probably deuterostomes and the Rhombozoa protostomes . This changeability of phyla has led some biologists to call for the concept of a phylum to be abandoned in favour of placing taxa in clades without any formal ranking of group size. A definition of
3528-474: The parasites (similar to entosis ), which divide to produce sporozoites that enter its cells. Eventually, the cells burst, releasing merozoites , which infect new cells. This may occur several times, until gamonts are produced, forming gametes that fuse to create new cysts. Many variations occur on this basic pattern, however, and many Apicomplexa have more than one host. The apical complex includes vesicles called rhoptries and micronemes , which open at
3591-636: The plant kingdom Plantae contains about 14 phyla, and the fungus kingdom Fungi contains about 8 phyla. Current research in phylogenetics is uncovering the relationships among phyla within larger clades like Ecdysozoa and Embryophyta . The term phylum was coined in 1866 by Ernst Haeckel from the Greek phylon ( φῦλον , "race, stock"), related to phyle ( φυλή , "tribe, clan"). Haeckel noted that species constantly evolved into new species that seemed to retain few consistent features among themselves and therefore few features that distinguished them as
3654-469: The relationships between groups. So phyla can be merged or split if it becomes apparent that they are related to one another or not. For example, the bearded worms were described as a new phylum (the Pogonophora) in the middle of the 20th century, but molecular work almost half a century later found them to be a group of annelids , so the phyla were merged (the bearded worms are now an annelid family ). On
3717-625: The transfer of a histone H4 lysine 20 (H4K20) modifier , KMT5A (Set8), from an animal host to the ancestor of apicomplexans. A second gene—H3K36 methyltransferase (Ashr3 in plants )—may have also been horizontally transferred. Within the Apicomplexa are three suborders of parasites: Within the Adelorina are species that infect invertebrates and others that infect vertebrates . The Eimeriorina—the largest suborder in this phylum—the lifecycle involves both sexual and asexual stages. The asexual stages reproduce by schizogony. The male gametocyte produces
3780-471: The vertebrate host. Microgametes and macrogametes are always found in the blood. The gametes are taken up by the insect vector during a blood meal. The microgametes migrate within the gut of the insect vector and fuse with the macrogametes. The fertilized macrogamete now becomes an ookinete , which penetrates the body of the vector. The ookinete then transforms into an oocyst and divides initially by meiosis and then by mitosis (haplontic lifecycle) to give rise to
3843-586: Was also thought to be sporozoan. Not all of these groups had spores, but all were parasitic. However, other parasitic or symbiotic unicellular organisms were included too in protozoan groups outside Sporozoa ( Flagellata , Ciliophora and Sarcodina ), if they had flagella (e.g., many Kinetoplastida , Retortamonadida , Diplomonadida , Trichomonadida , Hypermastigida ), cilia (e.g., Balantidium ) or pseudopods (e.g., Entamoeba , Acanthamoeba , Naegleria ). If they had cell walls, they also could be included in plant kingdom between bacteria or yeasts . Sporozoa
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#17328586097643906-478: Was created by Leuckart in 1879 and adopted by Bütschli in 1880. Through history, it grouped with the current Apicomplexa many unrelated groups. For example, Kudo (1954) included in the Sporozoa species of the Ascetosporea ( Rhizaria ), Microsporidia ( Fungi ), Myxozoa ( Animalia ), and Helicosporidium ( Chlorophyta ), while Zierdt (1978) included the genus Blastocystis ( Stramenopiles ). Dermocystidium
3969-703: Was seen by Antonie van Leeuwenhoek , who in 1674 saw probably oocysts of Eimeria stiedae in the gall bladder of a rabbit . The first species of the phylum to be described, Gregarina ovata , in earwigs ' intestines, was named by Dufour in 1828. He thought that they were a peculiar group related to the trematodes , at that time included in Vermes . Since then, many more have been identified and named. During 1826–1850, 41 species and six genera of Apicomplexa were named. In 1951–1975, 1873 new species and 83 new genera were added. The older taxon Sporozoa, included in Protozoa ,
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