View source for Apicomplexa

{{Short description|Phylum of parasitic alveolates}}
{{Automatic taxobox
| image = Apicomplexa Composite Image.png
| taxon = Apicomplexa
| authority = Levine, 1970<ref name="Levine1970">{{cite journal |author=Levine ND |title=Taxonomy of the Sporozoa |journal=J Parasitol |volume=56 |issue=4, Sect. 2, Part 1: Supplement: Proceedings Of the Second International Congress of Parasitology |pages=208–9 |year=1970 |jstor=3277701 }}</ref><ref>{{cite journal |author=Levine ND |title=Uniform Terminology for the Protozoan Subphylum Apicomplexa |journal=J Eukaryot Microbiol |volume=18 |issue=2 |pages=352–5 |date=May 1971 |doi=10.1111/j.1550-7408.1971.tb03330.x }}</ref>
| subdivision_ranks = Classes and subclasses <small>Perkins, 2000</small>
| subdivision = * [[Aconoidasida]] (= Hematozoa)
* [[Conoidasida]]
** [[Coccidia]]<br /> (= [[Coccidiasina]])
** [[Gregarinia]]<br /> (= [[Gregarinasina]])
| synonyms = *Apicomplexia
}}

The '''Apicomplexa''' (also called '''Apicomplexia'''; single: '''apicomplexan''') are organisms of a large [[phylum]] of mainly [[parasitic]] [[Alveolata|alveolate]]s. Most possess a unique form of [[organelle#Eukaryotic organelles|organelle]] structure that comprises a type of non-photosynthetic [[plastid]] called an [[apicoplast]]{{mdash}}with an [[cell membrane#Intracellular membranes|apical complex membrane]]. The organelle's apical shape is an adaptation that the apicomplexan applies in penetrating a host cell.

The Apicomplexa are unicellular and spore-forming. Most are [[obligate parasite|obligate]] [[parasitism#types|endoparasite]]s of animals,<ref>{{cite book |author=Jadwiga Grabda |title=Marine fish parasitology: an outline |page=8 |year=1991 |publisher=VCH |isbn=978-0-89573-823-3 }}</ref> except ''[[Nephromyces]]'', a [[symbiosis|symbiont]] in marine animals, originally classified as a [[chytrid]] fungus,<ref>{{cite journal |author1=Saffo M. B. |author2=McCoy A. M. |author3=Rieken C. |author4=Slamovits C. H. | year = 2010 | title = Nephromyces, a beneficial apicomplexan symbiont in marine animals | journal = Proceedings of the National Academy of Sciences | volume = 107 | issue = 37 | pages = 16190–5 | pmid = 20736348 | doi=10.1073/pnas.1002335107 | pmc=2941302 |bibcode=2010PNAS..10716190S |doi-access=free }}</ref> and the [[Chromerida]], some of which are [[Photosynthesis|photosynthetic]] partners of corals. Motile structures such as [[flagellum|flagella]] or [[pseudopod]]s are present only in certain [[gamete]] stages.

The Apicomplexa are a diverse group that includes organisms such as the [[coccidia]], [[gregarine]]s, [[piroplasm]]s, [[haemogregarine]]s, and [[Plasmodiidae|plasmodia]].
Diseases caused by Apicomplexa include:
* [[Babesiosis]] (''[[Babesia]]'')
* [[Malaria]] (''[[Plasmodium]]'')
* [[Cryptosporidiosis]] (''[[Cryptosporidium parvum]]'')
* [[Cyclosporiasis]] (''[[Cyclospora cayetanensis]]'')
* [[Cystoisosporiasis]] (''[[Cystoisospora belli]]'')
* [[Toxoplasmosis]] (''[[Toxoplasma gondii]]'')

The name Apicomplexa derives from two [[Latin]] words—''apex'' (top) and ''complexus'' (infolds)—for the set of [[organelle]]s 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 the Apicomplexa can use [[gliding motility]],<ref>{{cite journal |last=Kappe |first=Stefan H.I. |title=Apicomplexan gliding motility and host cell invasion: overhauling the motor model |journal=Trends in Parasitology |volume=20 |issue=1 |pages=13–16 |date=January 2004 |pmid=14700584 |doi=10.1016/j.pt.2003.10.011 |url=http://www.cell.com/trends/parasitology/abstract/S1471-4922(03)00287-3 |display-authors=etal|citeseerx=10.1.1.458.5746 }}</ref> that uses adhesions and small static myosin motors.<ref>{{cite journal |last1=Sibley |first1=L.D.I. |title=How apicomplexan parasites move in and out of cells |journal=Curr Opin Biotechnol |date=Oct 2010 |volume=21 |issue=5 |pages=592–598 |doi=10.1016/j.copbio.2010.05.009 |pmid=20580218 |pmc=2947570}}</ref> The other main lines of this obsolete grouping were the [[Ascetosporea]] (a group of [[Rhizaria]]), the [[Myxozoa]] (highly derived [[cnidarian]] [[animal]]s), and the [[Microsporidia]] (derived from [[fungus|fungi]]). Sometimes, the name Sporozoa is taken as a synonym for the Apicomplexa, or occasionally as a subset.

==Description==
[[File:Ookinete, sporozoite, merozoite.png|thumb|Some cell types: ookinete, sporozoite, merozoite]]

The phylum Apicomplexa contains all eukaryotes with a group of structures and organelles collectively termed the apical complex<!--helpfully redirects here, so don't link it-->.<ref name=EOL>{{cite web |url=http://tolweb.org/Apicomplexa/2446 |access-date=23 January 2019 |title=Apicomplexa, Levine 1970 |vauthors=Slapeta J, Morin-Adeline V |website=Tree of Life Web Project |date=2011}}</ref> This complex consists of structural components and [[Secretion#In eukaryotic cells|secretory organelles]] required for invasion of [[Host (biology)|host]] [[Cell (biology)|cell]]s during the parasitic stages of the [[Apicomplexan life cycle]].<ref name=EOL/> Apicomplexa have complex life cycles, involving several stages and typically undergoing both [[Asexual reproduction|asexual]] and [[Sexual reproduction|sexual replication]].<ref name=EOL/> All Apicomplexa are [[obligate parasite]]s for some portion of their life cycle, with some parasitizing two separate hosts for their asexual and sexual stages.<ref name=EOL/>

Besides 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.<ref name=EOL/> Like other eukaryotes, Apicomplexa have a [[cell nucleus|nucleus]], [[endoplasmic reticulum]] and [[Golgi complex]].<ref name=EOL/> Apicomplexa generally have a single mitochondrion, as well as another [[Symbiogenesis|endosymbiont-derived]] organelle called the [[apicoplast]] which maintains a separate 35 [[kilobase]] circular genome (with the exception of ''[[Cryptosporidium]]'' species and ''Gregarina niphandrodes'' which lack an apicoplast).<ref name=EOL/>

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 [[microtubule]]s (the [[conoid (organelle)|conoid]]), a secretory body (the [[rhoptry]]) and one or more polar rings. Additional slender electron-dense secretory bodies ([[microneme]]s) 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 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.{{citation needed|date=May 2021}}
* [[Flagellum|Flagella]] are found only in the motile gamete. These are posteriorly directed and vary in number (usually one to three).
* [[Basal body|Basal bodies]] are present. Although hemosporidians and piroplasmids have normal triplets of [[microtubule]]s in their basal bodies, coccidians and gregarines have nine singlets.
* The [[mitochondria]] have tubular [[cristae]].
* [[Centriole]]s, [[chloroplast]]s, ejectile organelles, and inclusions are absent.
* The cell is surrounded by a [[pellicle (biology)|pellicle]] of three membrane layers (the alveolar structure) penetrated by micropores.

[[File:2023 Apicomplexan.svg|center|thumb|upright=2|{{center|'''Apicomplexan structure'''<ref>{{Cite journal |author-link1=Patrick J. Keeling |author1=Patrick J. Keeling |author2=Yana Eglit |doi=10.1371/JOURNAL.PBIO.3002395 |doi-access=free |issn=1544-9173 |issue=11 |journal=[[PLOS Biology]] |language=en |article-number=e3002395 |pmc=10662721 |pmid=37988341 |date=21 November 2023 |title=Openly available illustrations as tools to describe eukaryotic microbial diversity |volume=21}}</ref>}}{{ordered list|Anterior [[Polar organelle|polar]] ring|
Intra-conoid [[microtubules]]|
Conoid|
Posterior polar ring|
Inner membrane complex|
Subpellicular microtubules|
[[Rhoptry|Rhoptries]], hold [[Enzyme|enzymes]] released during host penetration|
[[Microneme|Micronemes]], important for host-cell invasion and [[gliding motility]]|
[[Mitochondria|Mitochondrion]], creates [[Adenosine triphosphate|ATP]] (energy) for the cell (tubular cristae)|
Micropore|
Dense granules|
[[Apicoplast]] membranes (4, secondary red, non-photosynthetic)|
[[Golgi apparatus]]; modifies [[protein]]s and sends them out of the cell|
[[Cell nucleus|Nucleus]]|
[[Endoplasmic reticulum]], the transport network for molecules going to specific parts of the cell|
}}]]

Replication:
* [[Mitosis]] is usually closed, with an intranuclear spindle; in some species, it is open at the poles.
* Cell division is usually by [[schizogony]].
* [[Meiosis]] occurs in the [[zygote]].

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.<ref>{{Cite journal|last=Sibley|first=L. D.|date=2004-04-09|title=Intracellular Parasite Invasion Strategies|url=https://www.science.org/doi/10.1126/science.1094717|journal=Science|language=en|volume=304|issue=5668|pages=248–253|doi=10.1126/science.1094717|pmid=15073368|bibcode=2004Sci...304..248S|s2cid=23218754|issn=0036-8075|url-access=subscription}}</ref>

Other features common to this phylum are 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]]''.<ref name=Templeton2010/>

==Life cycle==
{{Further|Apicomplexa lifecycle stages}}
{{multiple image
| direction = vertical
| width = 260
| image1 =Apicomplexa life cycle v2.svg
| alt1 =
| caption1 =Generic lifecycle of an Apicomplexan: 1-[[zygote]] ([[Microbial cyst|cyst]]), 2-[[sporozoite]]s, 3-[[merozoite]]s, 4-[[gametocyte]]s
}}

Most members have a complex lifecycle, involving both asexual and sexual reproduction.  Typically, a host is infected via an active invasion by the parasites (similar to [[entosis]]), which divide to produce [[sporozoite]]s 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.<ref>{{Cite journal |last1=Templeton |first1=Thomas J. |last2=Iyer |first2=Lakshminarayan M. |last3=Anantharaman |first3=Vivek |last4=Enomoto |first4=Shinichiro |last5=Abrahante |first5=Juan E. |last6=Subramanian |first6=G.M. |last7=Hoffman |first7=Stephen L. |last8=Abrahamsen |first8=Mitchell S. |last9=Aravind |first9=L. |date=September 2004 |title=Comparative Analysis of Apicomplexa and Genomic Diversity in Eukaryotes |journal=Genome Research |volume=14 |issue=9 |pages=1686–1695 |doi=10.1101/gr.2615304 |issn=1088-9051 |pmid=15342554|pmc=515313 }}</ref>

The apical complex includes [[Vesicle (biology)|vesicle]]s called [[rhoptries]] and [[microneme]]s, which open at the anterior of the cell.  These secrete enzymes that allow the parasite to enter other cells.  The tip is surrounded by a band of [[microtubule]]s, called the polar ring, and among the Conoidasida is also a funnel of tubulin proteins called the conoid.<ref name=coccidiaworld>{{cite web|url=http://biology.unm.edu/biology/coccidia/home.html|title=The Coccidia of the World|last1=Duszynski|first1=Donald W.|first2=Steve J.|last2=Upton|first3=Lee|last3=Couch|publisher=Department of Biology, University of New Mexico, and Division of Biology, Kansas State University|date=2004-02-21|format=Online database|access-date=2006-10-04|archive-url=https://web.archive.org/web/20101230215149/http://biology.unm.edu/biology/coccidia/home.html|archive-date=2010-12-30}}</ref>   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.<ref name="Angel. 2018">{{Cite book|last=Angel.|first=Sherman|title=Medical Parasitology|date=2018|publisher=EDTECH|isbn=978-1-83947-353-1|oclc=1132400230}}</ref>

The presence of alveoli and other traits place the Apicomplexa among a group called the [[alveolate]]s. Several related flagellates, such as ''[[Perkinsus marinus|Perkinsus]]'' and ''[[Colpodella]]'', have structures similar to the polar ring and were formerly included here, but most appear to be closer relatives of the [[dinoflagellate]]s.  They are probably similar to the common ancestor of the two groups.<ref name="Angel. 2018"/>

Another similarity is that many apicomplexan cells contain a single [[plastid]], called 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 alga|green]].<ref>{{cite journal | journal = American Journal of Botany | year = 2004 | volume = 91 | pages = 1481–1493 | title = Diversity and evolutionary history of plastids and their hosts | author = Patrick J. Keeling | doi = 10.3732/ajb.91.10.1481 | issue=10 | pmid=21652304| doi-access = free }}</ref><ref>{{cite journal | doi = 10.1093/nar/gkn483 |date=July 2008 |author1=Ram, Ev |author2=Naik, R |author3=Ganguli, M |author4=Habib, S | title = DNA organization by the apicoplast-targeted bacterial histone-like protein of Plasmodium falciparum | volume =  36| issue =  15| pages =  5061–73| pmid = 18663012 | journal = Nucleic Acids Research | pmc = 2528193 }}</ref>

==Subgroups==
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.<ref name="Mathur_2021"/>

''Perkinsus '', while once considered a member of the Apicomplexa, has been moved to a new phylum — [[Perkinsozoa]].<ref>{{cite journal|last1=Norén|first1=Fredrik|last2=Moestrup|first2=Øjvind|last3=Rehnstam-Holm|first3=Ann-Sofi|title=Parvilucifera infectans norén et moestrup gen. et sp. nov. (perkinsozoa phylum nov.): a parasitic flagellate capable of killing toxic microalgae|journal=European Journal of Protistology|date=October 1999|volume=35|issue=3|pages=233–254|doi=10.1016/S0932-4739(99)80001-7}}</ref>

===Gregarines===
[[File:Septate gregarine.jpg|thumb|right|100px|Trophozoite of a gregarine]]
{{Main|Gregarinasina}}
The gregarines are generally parasites of [[annelid]]s, [[arthropod]]s, and [[Mollusca|molluscs]]. They are often found in the [[Gut (anatomy)|gut]]s 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 [[merozoite]]s by [[schizogony]]. The [[merozoite]]s are released by lysing the host cell, which in turn invade other cells. At some point in the apicomplexan lifecycle, [[gametocyte]]s are formed. These are released by lysis of the host cells, which group together. Each gametocyte forms multiple [[gamete]]s. The gametes fuse with another to form [[oocyst]]s. The oocysts leave the host to be taken up by a new host.<ref>{{Cite journal |last1=Wong |first1=Wesley |last2=Wenger |first2=Edward A. |last3=Hartl |first3=Daniel L. |last4=Wirth |first4=Dyann F. |date=2018-01-09 |title=Modeling the genetic relatedness of Plasmodium falciparum parasites following meiotic recombination and cotransmission |journal=PLOS Computational Biology |volume=14 |issue=1 |article-number=e1005923 |doi=10.1371/journal.pcbi.1005923 |pmid=29315306 |pmc=5777656 |bibcode=2018PLSCB..14E5923W |issn=1553-7358 |doi-access=free }}</ref>

===Coccidians===
[[File:Toxoplasma gondii.jpg|thumb|150px|Dividing ''[[Toxoplasma gondii]]'' (Coccidia) parasites]]
{{Main|Coccidia}}
In general, coccidians are parasites of [[vertebrate]]s. Like gregarines, they are commonly parasites of 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 [[microgamete]]s (anisogamy). The microgametes are motile and must reach the macrogamete to fertilize it. The fertilized macrogamete forms 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.<ref>{{Cite journal |last1=Adl |first1=Sina M. |last2=Bass |first2=David |last3=Lane |first3=Christopher E. |last4=Lukeš |first4=Julius |last5=Schoch |first5=Conrad L. |last6=Smirnov |first6=Alexey |last7=Agatha |first7=Sabine |last8=Berney |first8=Cedric |last9=Brown |first9=Matthew W. |last10=Burki |first10=Fabien |last11=Cárdenas |first11=Paco |last12=Čepička |first12=Ivan |last13=Chistyakova |first13=Lyudmila |last14=Campo |first14=Javier |last15=Dunthorn |first15=Micah |date=2019 |title=Revisions to the Classification, Nomenclature, and Diversity of Eukaryotes |journal=Journal of Eukaryotic Microbiology |language=en |volume=66 |issue=1 |pages=4–119 |doi=10.1111/jeu.12691 |pmid=30257078 |pmc=6492006 |issn=1066-5234}}</ref>

The main difference between the coccidians and the gregarines is in the gamonts. In the coccidia, these are small, intracellular, and without epimerites or [[mucron]]s. In 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.<ref>{{Cite journal |last1=Cruz-Bustos |first1=Teresa |last2=Feix |first2=Anna Sophia |last3=Ruttkowski |first3=Bärbel |last4=Joachim |first4=Anja |date=2021-10-04 |title=Sexual Development in Non-Human Parasitic Apicomplexa: Just Biology or Targets for Control? |journal=Animals |language=en |volume=11 |issue=10 |page=2891 |doi=10.3390/ani11102891 |pmid=34679913 |pmc=8532714 |issn=2076-2615|doi-access=free }}</ref>

===Haemosporidia===
[[File:Immature and mature trophozoites of the Plasmodium vivax parasite PHIL 2720 lores.jpg|thumb|150px|upright=1.3|Trophozoites of the ''[[Plasmodium vivax]]'' (Haemosporidia) parasite among human red blood cells]]
{{Main|Haemosporida}}
The Haemosporidia have more complex lifecycles that alternate between an arthropod and a vertebrate host. The trophozoite parasitises [[erythrocyte]]s or other tissues in 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 the [[sporozoite]]s. 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.<ref>{{Cite journal |last1=Frischknecht |first1=Friedrich |last2=Matuschewski |first2=Kai |date=2017-01-20 |title=''Plasmodium'' Sporozoite Biology |journal=Cold Spring Harbor Perspectives in Medicine |language=en |volume=7 |issue=5 |article-number=a025478 |doi=10.1101/cshperspect.a025478 |pmid=28108531 |pmc=5411682 |issn=2157-1422}}</ref>

===Marosporida===
The class Marosporida <small>Mathur, Kristmundsson, Gestal, Freeman, and Keeling 2020</small> is a newly recognized lineage of apicomplexans that is sister to the Coccidia and Hematozoa. It is defined as a phylogenetic [[clade]] containing ''Aggregata octopiana'' <small>Frenzel 1885</small>, ''[[Merocystis kathae]]'' <small>Dakin, 1911</small> (both Aggregatidae, originally coccidians), ''[[Rhytidocystis]]'' sp. 1 and ''Rhytidocystis'' sp. 2 <small>Janouškovec et al. 2019</small> ([[Rhytidocystidae]] <small>Levine, 1979</small>, originally coccidians, [[Agamococcidiorida]]), and ''Margolisiella islandica'' <small>Kristmundsson et al. 2011</small> (closely related to Rhytidocystidae). Marosporida infect marine invertebrates. Members of this clade retain [[plastid]] genomes and 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.<ref name="Mathur_2021">{{cite journal |last1=Mathur |first1=Varsha |last2=Kwong |first2=Waldan K. |last3=Husnik |first3=Filip |last4=Irwin |first4=Nicholas A. T. |last5=Kristmundsson |first5=Árni |last6=Gestal |first6=Camino |last7=Freeman |first7=Mark |last8=Keeling |first8=Patrick J |title=Phylogenomics Identifies a New Major Subgroup of Apicomplexans, Marosporida ''class nov''., with Extreme Apicoplast Genome Reduction |journal=Genome Biology and Evolution |date=18 November 2020 |volume=13 |issue=2: evaa244 |article-number=evaa244 |doi=10.1093/gbe/evaa244 |url= |publisher=Oxford University Press |pmid=33566096 |pmc=7875001 |issn=1759-6653}}</ref>

==Ecology and distribution==
[[File:Parasite140105-fig3 Toxoplasmosis in a bar-shouldered dove - TEM of 2 tachyzoites.tif|thumb|Two tachyzoites of ''[[Toxoplasma gondii]]'', transmission electron microscopy]]
Many of the apicomplexan parasites are important pathogens of humans and domestic animals. In contrast to [[bacteria]]l pathogens, these apicomplexan parasites are [[Eukaryote|eukaryotic]] and share many metabolic pathways with their animal hosts. This makes therapeutic target development extremely difficult – a drug that harms an apicomplexan parasite is also likely to harm its human host. At present, no effective [[vaccine]]s 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 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]]<ref>{{cite web |url=http://eupathdb.org |title=EuPathDB |access-date=2012-01-02}}</ref> family of websites, which currently provides specialised services for ''[[Plasmodium]]'' species ([[PlasmoDB]]),<ref>{{Cite journal | last1 = Bahl | first1 = A. | last2 = Brunk | first2 = B. | last3 = Crabtree | first3 = J. | last4 = Fraunholz | first4 = M. J. | last5 = Gajria | first5 = B. | last6 = Grant | first6 = G. R. | last7 = Ginsburg | first7 = H. | last8 = Gupta | first8 = D. | last9 = Kissinger | first9 = J. C. | last10 = Labo | first10 = P. | last11 = Li | first11 = L. | last12 = Mailman | first12 = M. D. | last13 = Milgram | first13 = A. J. | last14 = Pearson | first14 = D. S. | last15 = Roos | first15 = D. S. | last16 = Schug | first16 = J. | last17 = Stoeckert Jr | first17 = C. J. | last18 = Whetzel | first18 = P. | title = PlasmoDB: The Plasmodium genome resource. A database integrating experimental and computational data | journal = Nucleic Acids Research | volume = 31 | issue = 1 | pages = 212–215 | year = 2003 | pmid = 12519984 | pmc = 165528 | doi=10.1093/nar/gkg081}}</ref><ref>{{cite web |url=http://plasmodb.org |title=PlasmoDB |access-date=2012-01-02}}</ref> [[coccidia]]ns (ToxoDB),<ref>{{Cite journal | last1 = Kissinger | first1 = J. C. | last2 = Gajria | first2 = B. | last3 = Li | first3 = L. | last4 = Paulsen | first4 = I. T. | last5 = Roos | first5 = D. S. | title = ToxoDB: Accessing the Toxoplasma gondii genome | journal = Nucleic Acids Research | volume = 31 | issue = 1 | pages = 234–236 | year = 2003 | pmid = 12519989 | pmc = 165519 | doi=10.1093/nar/gkg072}}</ref><ref>{{cite web |url=http://toxodb.org |title=ToxoDB |access-date=2012-01-02}}</ref> [[piroplasms]] (PiroplasmaDB),<ref>{{cite web |url=http://piroplasmadb.org |title=PiroplasmaDB |access-date=2012-01-02}}</ref> and ''[[Cryptosporidium]]'' species (CryptoDB).<ref>{{Cite journal | last1 = Heiges | first1 = M. | last2 = Wang | first2 = H. | last3 = Robinson | first3 = E. | last4 = Aurrecoechea | first4 = C. | last5 = Gao | first5 = X. | last6 = Kaluskar | first6 = N. | last7 = Rhodes | first7 = P. | last8 = Wang | first8 = S. | last9 = He | first9 = C. Z. | last10 = Su | first10 = Y. | last11 = Miller | first11 = J. | last12 = Kraemer | first12 = E. | last13 = Kissinger | first13 = J. C. | title = CryptoDB: A Cryptosporidium bioinformatics resource update | doi = 10.1093/nar/gkj078 | journal = Nucleic Acids Research | volume = 34 | issue = 90001 | pages = D419–D422 | year = 2006 | pmid = 16381902 | pmc =1347441 }}</ref><ref>{{cite web |url=http://cryptodb.org |title=CryptoDB |access-date=2012-01-02}}</ref> One possible target for drugs is the plastid, and in fact existing drugs such as [[Tetracycline antibiotics|tetracycline]]s, which are effective against apicomplexans, seem to operate against the plastid.<ref>{{cite journal | doi = 10.1128/AAC.00394-06 |date=September 2006 |author1=Dahl, El |author2=Shock, Jl |author3=Shenai, Br |author4=Gut, J |author5=Derisi, Jl |author6=Rosenthal, Pj | title = Tetracyclines specifically target the apicoplast of the malaria parasite Plasmodium falciparum | volume = 50 | issue = 9 | pages = 3124–31 | pmid = 16940111 | pmc = 1563505 | journal = Antimicrobial Agents and Chemotherapy }}</ref>

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 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 the likelihood of transmission have evolved in multiple genera. Polyenergid [[oocyst]]s and tissue cysts are found in representatives of the orders [[Protococcidiorida]] and [[Eimeriida]]. [[Hypnozoite]]s 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 the transfer of a [[histone H4]] lysine 20 (H4K20) [[Histone#Chromatin regulation|modifier]], [[KMT5A]] (Set8), from an animal host to the ancestor of apicomplexans.<ref name=Kishore2013>{{cite journal |vauthors=Kishore SP, Stiller JW, Deitsch KW |title=Horizontal gene transfer of epigenetic machinery and evolution of parasitism in the malaria parasite ''Plasmodium falciparum'' and other apicomplexans |journal=BMC Evol. Biol. |volume=13 |article-number=37 |year=2013 |issue=1 |pmid=23398820 |pmc=3598677 |doi=10.1186/1471-2148-13-37 |bibcode=2013BMCEE..13...37K |doi-access=free }}</ref> A second gene—H3K36 methyltransferase (Ashr3 in [[plant]]s)—may have also been horizontally transferred.<ref name="Angel. 2018"/>

=== Blood-borne genera ===

Within the Apicomplexa are three suborders of parasites:<ref name="Angel. 2018"/>
* suborder [[Adeleorina]]—eight genera
* suborder [[Laveraniina]] (formerly Haemosporina)—all genera in this suborder
* suborder [[Eimeriorina]]—two genera (''[[Lankesterella]]'' and ''[[Schellackia]]'')

Within the Adelorina are species that infect [[invertebrate]]s and others that infect [[vertebrate]]s. 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 a large number of gametes and the zygote gives rise to an oocyst, which is the infective stage. The majority are [[Monoxenous development|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.

==Taxonomy==
{{Further|wikispecies:Apicomplexa}}

===History===
The first Apicomplexa protozoan was seen by [[Antonie van Leeuwenhoek]], who in 1674 saw probably [[oocyst]]s of ''[[Eimeria stiedae]]'' in the [[gall bladder]] of a [[rabbit]]. The first species of the [[phylum]] to be described, ''[[Gregarina ovata]]'', in [[earwig]]s' intestines, was named by Dufour in 1828. He thought that they were a peculiar group related to the [[trematode]]s, at that time included in [[Vermes]].<ref name="Levine (1988b)" /> 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.<ref name="Levine (1988b)">{{cite journal | author = Levine N. D. | year = 1988 | title = Progress in taxonomy of the Apicomplexan protozoa | journal = The Journal of Protozoology | volume = 35 | issue = 4| pages = 518–520 |pmid=3143826 | doi=10.1111/j.1550-7408.1988.tb04141.x}}</ref>

The older taxon Sporozoa, included in [[Protozoa]], was created by [[Rudolf Leuckart|Leuckart]] in 1879<ref>{{cite book |first=R. |last=Leuckart |title=Die menschlichen Parasiten |publisher=Winter |location=Leipzig |year=1879 |edition=2nd |volume=1 |url=https://www.europeana.eu/portal/record/9200143/BibliographicResource_2000069323145.html}}</ref> and adopted by [[Otto Bütschli|Bütschli]] in 1880.<ref>Bütschli, O. (1880-82). ''Dr. H.G. Bronn's Klassen und Ordnungen des Thier-Reichs''. Erster Band: Protozoa. Abt. I, Sarkodina und Sporozoa, [https://archive.org/details/drhgbronnsklasse0101bron].</ref> 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]]).<ref>{{cite journal |first=G. |last=Perez-Cordon |display-authors=etal |title=Finding of ''Blastocystis'' sp. in bivalves of the genus ''Donax'' |journal=Rev. Peru. Biol. |volume=14 |issue=2 |pages=301–2 |year=2007 |doi=10.15381/rpb.v14i2.1824 |doi-access=free }}</ref> ''[[Dermocystidium]]'' was also thought to be sporozoan. Not all of these groups had spores, but all were parasitic.<ref name="Levine (1988b)" /> 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 [[yeast]]s.

Sporozoa is no longer regarded as biologically valid and its use is discouraged,<ref>{{cite web |url=http://www.ucmp.berkeley.edu/protista/apicomplexa.html |title=Introduction to the Apicomplexa |access-date=2009-05-31| archive-url= https://web.archive.org/web/20090420123252/http://ucmp.berkeley.edu/protista/apicomplexa.html| archive-date= 20 April 2009 | url-status= live}}</ref> 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.<ref name="Levine1970" />

By 1987, a comprehensive survey of the phylum was completed: in all, 4516 species and 339 genera had been named. They consisted of:<ref name="Levine (1988a)">{{cite book |first=N.D. |last=Levine |title=The protozoan phylum Apicomplexa |publisher=CRC Press |year=1988 |isbn=978-0-8493-4653-8 }}</ref><ref name="Levine (1988b)" />
* Class [[Conoidasida]]
** Subclass [[Gregarinasina]] ''[[pro parte|p.p.]]''
*** Order [[Eugregarinorida]], with 1624 named species and 231 named genera
** Subclass [[Coccidiasina]] ''p.p''
*** Order [[Eucoccidiorida]] ''p.p''
**** Suborder [[Adeleorina]] ''p.p''
***** Group [[Hemogregarine]]s, with 399 species and four genera
**** Suborder [[Eimeriorina]], with 1771 species and 43 genera
* Class [[Aconoidasida]]
** Order [[Haemospororida]], with 444 species and nine genera
** Order [[Piroplasmorida]], with 173 species and 20 genera
* Other minor groups omitted above, with 105 species and 32 genera

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.<ref>{{Cite journal |last1=Karadjian |first1=Gregory |last2=Hassanin |first2=Alexandre |last3=Saintpierre |first3=Benjamin |last4=Gembu Tungaluna |first4=Guy-Crispin |last5=Ariey |first5=Frederic |last6=Ayala |first6=Francisco J. |last7=Landau |first7=Irene |last8=Duval |first8=Linda |date=2016-08-15 |title=Highly rearranged mitochondrial genome in Nycteria parasites (Haemosporidia) from bats |journal=Proceedings of the National Academy of Sciences |language=en |volume=113 |issue=35 |pages=9834–9839 |doi=10.1073/pnas.1610643113 |pmid=27528689 |pmc=5024609 |bibcode=2016PNAS..113.9834K |issn=0027-8424|doi-access=free }}</ref>

===Jacques Euzéby (1988)===
[[Jacques Euzéby]] in 1988<ref name="Euzéby1988">{{cite book |last=Euzéby |first=J. |title=Apicomplexa, 2: Hémosporidioses, Fascicule 1: Plasmodiidés, Haemoproteidés "Piroplasmes" (caractères généraux) |publisher=Fondation Marcel Merieux |series=Protozoologie Médicale Comparée |year=1988 |isbn=978-2-901773-73-3 |volume=3 |oclc=463445910}}</ref> created a new class [[Haemosporidiasina]] by merging subclass [[Piroplasmasina]] and suborder [[Haemospororina]].
* Subclass [[Gregarinasina]] (the gregarines)
* Subclass [[Coccidiasina]]
** Suborder [[Adeleorina]] (the adeleorins)
** Suborder [[Eimeriorina]] (the eimeriorins)
* Subclass [[Haemosporidiasina]]
** Order [[Achromatorida]]
** Order [[Chromatorida]]

The division into Achromatorida and Chromatorida, although proposed on morphological grounds, may have a biological basis, as the ability to store [[haemozoin]] appears to have evolved only once.<ref name=Martinsen2008>{{cite journal |vauthors=Martinsen ES, Perkins SL, Schall JJ |title=A three-genome phylogeny of malaria parasites (Plasmodium and closely related genera): evolution of life-history traits and host switches |journal=Mol. Phylogenet. Evol. |volume=47 |issue=1 |pages=261–73 |date=April 2008 |pmid=18248741 |doi=10.1016/j.ympev.2007.11.012 |bibcode=2008MolPE..47..261M }}</ref>

===Roberts and Janovy (1996)===
Roberts and Janovy in 1996 divided the phylum into the following subclasses and suborders (omitting classes and orders):<ref>{{cite book |last1=Roberts |first1=L. |last2=Janovy |first2=J. |title=Foundations of Parasitology |publisher=Wm. C. Brown |location=Dubuque IA |year=1996 |isbn=978-0-697-26071-0 |oclc=33439613 |edition=5th }}</ref>
* Subclass [[Gregarinasina]] (the gregarines)
* Subclass [[Coccidiasina]]
** Suborder [[Adeleorina]] (the adeleorins)
** Suborder [[Eimeriorina]] (the eimeriorins)
** Suborder [[Haemospororina]] (the haemospororins)
* Subclass [[Piroplasmasina]] (the piroplasms)
These form the following five taxonomic groups:
# The gregarines are, in general, one-host parasites of invertebrates.
# The adeleorins are one-host parasites of invertebrates or vertebrates, or two-host parasites that alternately infect haematophagous (blood-feeding) invertebrates and the blood of vertebrates.
# The eimeriorins are a diverse group that includes one host species of invertebrates, two-host species of invertebrates, one-host species of vertebrates and two-host species of vertebrates. The eimeriorins are frequently called the coccidia. This term is often used to include the adeleorins.
# Haemospororins, often known as the malaria parasites, are two-host Apicomplexa that parasitize blood-feeding [[dipteran]] flies and the blood of various tetrapod vertebrates.
# Piroplasms where all the species included are two-host parasites infecting ticks and vertebrates.

===Perkins (2000)===
[[File:Apicomplexa tree..png|thumb|right|300px]]

Perkins et al. proposed the following scheme.<ref name=Perkins2000>{{cite book |vauthors=Perkins FO, Barta JR, Clopton RE, Peirce MA, Upton SJ |chapter=Phylum Apicomplexa |veditors=Lee JJ, Leedale GF, Bradbury P |title=An Illustrated guide to the Protozoa: organisms traditionally referred to as protozoa, or newly discovered groups |publisher=Society of Protozoologists |edition=2nd |year=2000 |oclc=704052757 |isbn=978-1-891276-22-4  |pages=190–369 |volume=1}}</ref> It is outdated as the [[Perkinsidae]] have since been recognised as a sister group to the dinoflagellates rather that the Apicomplexia:
 
* Class [[Aconoidasida]]
*: ''Conoid present only in the [[ookinete]] of some species''
::*Order [[Haemospororida]]
:::''Macrogamete and microgamete develop separately. Syzygy does not occur. Ookinete has a conoid. Sporozoites have three walls. Heteroxenous: alternates between vertebrate host (in which merogony occurs) and invertebrate host (in which sporogony occurs). Usually blood parasites, transmitted by blood-sucking insects.''
::*Order [[Piroplasmorida]]
* Class [[Conoidasida]]
** Subclass [[Gregarinasina]]
*** Order [[Archigregarinorida]]
*** Order [[Eugregarinorida]]
**** Suborder [[Adeleorina]]
**** Suborder [[Eimeriorina]]
*** Order [[Neogregarinorida]]
** Subclass [[Coccidiasina]]
*** Order [[Agamococcidiorida]]
*** Order [[Eucoccidiorida]]
*** Order [[Ixorheorida]]
*** Order [[Protococcidiorida]]
* Class [[Perkinsasida]]
::*Order [[Perkinsorida]]
:::*Family [[Perkinsidae]]

The name Protospiromonadida has been proposed for the common ancestor of the Gregarinomorpha and Coccidiomorpha.<ref name=Krylov1992>{{cite journal |author=Krylov MV |title=[The origin of heteroxeny in Sporozoa] |language=ru |journal=Parazitologiia |volume=26 |issue=5 |pages=361–368 |year=1992 |pmid=1297964 }}</ref>

Another group of organisms that belong in this taxon are the corallicolids.<ref name=Kwong2019>{{cite journal | last1 = Kwong | first1 = WK | last2 = Del Campo | first2 = J | last3 = Mathur | first3 = V | last4 = Vermeij | first4 = MJA | last5 = Keeling | first5 = PJ | year = 2019 | title = A widespread coral-infecting apicomplexan with chlorophyll biosynthesis genes | journal = Nature | volume = 568 | issue = 7750| pages = 103–107 | doi = 10.1038/s41586-019-1072-z | pmid = 30944491 | bibcode = 2019Natur.568..103K | s2cid = 92996418 }}</ref> 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 a sister taxon to the Hematozoa.<ref name=Muñoz-Gómez2019>Muñoz-Gómez SA, Durnin K, Eme L, Paight C, Lane CE, Saffo MB, Slamovits CH (2019) ''Nephromyces'' represents a diverse and novel lineage of the Apicomplexa that has retained apicoplasts. Genome Biol Evol</ref> This genus is found in the renal sac of molgulid ascidian [[tunicate]]s.

== Evolution ==
{{Further|Alveolate#Phylogeny}}

Members of this phylum, except for the [[Photosynthesis|photosynthetic]] chromerids,<ref name="pmid18288187">{{cite journal |title=A photosynthetic alveolate closely related to apicomplexan parasites |journal=Nature |volume=451 |issue=7181 |pages=959–963 |date=February 2008 |pmid=18288187 |doi=10.1038/nature06635 |author1=Moore RB |author2=Oborník M  |author3=Janouskovec J |author4=Chrudimský T |author5=Vancová M |author6=Green DH |author7=Wright SW |author8=Davies NW |author9=Bolch CJ|display-authors=8 |last10=Heimann |first10=Kirsten |last11=Šlapeta |first11=Jan |last12=Hoegh-Guldberg |first12=Ove |last13=Logsdon |first13=John M. |last14=Carter |first14=Dee A. |bibcode=2008Natur.451..959M |s2cid=28005870 }}</ref> 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.<ref name=Kuvardina2002>{{cite journal |vauthors=Kuvardina ON, Leander BS, Aleshin VV, Myl'nikov AP, Keeling PJ, Simdyanov TG |title=The phylogeny of colpodellids (Alveolata) using small subunit rRNA gene sequences suggests they are the free-living sister group to apicomplexans |journal=J. Eukaryot. Microbiol. |volume=49 |issue=6 |pages=498–504 |date=November 2002 |pmid=12503687 |doi=10.1111/j.1550-7408.2002.tb00235.x |s2cid=4283969 }}</ref><ref name=Leander2002>{{cite journal |vauthors=Leander BS, Keeling PJ |title=Morphostasis in alveolate evolution |journal=Trends Ecol Evol |volume=18 |issue=8 |pages=395–402 |date=August 2003 |doi=10.1016/S0169-5347(03)00152-6 |citeseerx=10.1.1.410.9134 }}</ref> Further evolution of this phylum has been estimated to have occurred about {{Mya|800}}.<ref name=Escalante1995>{{cite journal |vauthors=Escalante AA, Ayala FJ |title=Evolutionary origin of Plasmodium and other Apicomplexa based on rRNA genes |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=92 |issue=13 |pages=5793–7 |date=June 1995 |pmid=7597031 |pmc=41587 |doi=10.1073/pnas.92.13.5793|bibcode=1995PNAS...92.5793E |doi-access=free }}</ref> The oldest extant clade is thought to be the archigregarines.<ref name="Kuvardina2002"/>

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.<ref name=Morrison2009>{{cite journal |author=Morrison DA |title=Evolution of the Apicomplexa: where are we now? |journal=Trends Parasitol. |volume=25 |issue=8 |pages=375–82 |date=August 2009 |pmid=19635681 |doi=10.1016/j.pt.2009.05.010 }}</ref> The Haemosporidia and the Piroplasma appear to be sister clades, and are more closely related to the coccidians than to the gregarines.<ref name=Templeton2010>{{cite journal |vauthors=Templeton TJ, Enomoto S, Chen WJ|display-authors=etal |title=A genome-sequence survey for Ascogregarina taiwanensis supports evolutionary affiliation but metabolic diversity between a ''Gregarine'' and ''Cryptosporidium'' |journal=Mol. Biol. Evol. |volume=27 |issue=2 |pages=235–48 |date=February 2010 |pmid=19778951 |pmc=2877549 |doi=10.1093/molbev/msp226 |url=}}</ref> Marosporida is a sister group to Coccidiomorphea.<ref name="Mathur_2021"/>

{{clade| style=font-size:85%;line-height:85%
|label1= [[Myzozoa]]
|1={{clade
   |label1= '''Apicomplexa''' s.l.
   |1={{clade
      |1=Squirmida (''[[Digyalum]]'', ''[[Filipodium]]'', ''[[Platyproteum]]'')
      |2={{clade
         |label1=[[Chrompodellids]]/[[Apicomonadea]]
         |1={{clade
            |1= [[Chromerida]] (''[[Chromera velia|Chromera]]'', ''[[Vitrella brassicaformis|Vitrella]]'', ''[[Piridium]]'')
            |2= [[Colpodellida]] (''[[Colpodella]]'')
            |3= [[Voromonadida]] (''[[Alphamonas]]'', ''[[Voromonas]]'')
            }}
         |label2= Apicomplexa s.s.
         |2={{clade
            |label1='''[[Gregarinasina|Gregarines]]''' s.l.
            |1={{clade
               |1= ''[[Cryptosporidium]]''
               |2= Gregarines s.s.
               }}
            |2={{clade
               |label1= '''Marosporida'''
               |1={{clade
                  |1= Aggregatidae (''[[Aggregata]]'', ''[[Merocystis]]'')
                  |2={{clade
                     |1=''[[Margolisiella]]''
                     |2= Rhytidocystidae (''[[Rhytidocystis]]'')
                     }}
                  }}
               |label2=Coccidiomorphea
               |2={{clade
                  |label1= '''Coccidia'''
                  |1={{clade
                     |1= [[Hemogregarines]]
                     |2= Coccidia with a single host (''[[Eimeria]]'', ''[[Isospora]]'', ''[[Cyclospora]]'')
                     |3= Cyst-forming coccidia (''[[Toxoplasma]]'', ''[[Sarcocystis]]'', ''[[Frenkellia]]'')
                     }}
                  |label2= Hematozoa
                  |2={{clade
                     |1= Piroplasms (''[[Babesia]]'', ''[[Theileria]]'')
                     |2= '''Hemosporidia''' (''[[Plasmodium]]'', ''[[Leucocytozoon]]'')
                     }}
                  }}
               }}
            }}
         }}
      }}
   |2= [[Dinoflagellates]] & [[Perkinsozoa]]
   }}
}}

Janouškovec et al. 2015 presents a somewhat different phylogeny, supporting the work of others showing multiple events of [[plastid]]s losing photosynthesis. More importantly this work provides the first [[phylogenetic]] evidence that there have also been multiple events of plastids becoming genome-free.<ref name="Smith-Keeling-2016">{{cite journal | last1=Smith | first1=David Roy | last2=Keeling | first2=Patrick J. | title=Protists and the Wild, Wild West of Gene Expression: New Frontiers, Lawlessness, and Misfits | journal=[[Annual Review of Microbiology]] | publisher=[[Annual Reviews (publisher)|Annual Reviews]] | volume=70 | issue=1 | date=2016-09-08 | issn=0066-4227 | doi=10.1146/annurev-micro-102215-095448 | pages=161–178| pmid=27359218 | doi-access=free }}</ref>

== See also ==
*[[Centrocone]]

== References ==
{{Reflist}}

==External links==
* {{cite web  | first = S.J.  | last = Brands  | title = The Taxonomicon & Systema Naturae  | work = Taxon: Genus Cryptosporidium  | publisher = Universal Taxonomic Services  | location = Amsterdam, the Netherlands  | year = 2000  | url = http://www.taxonomy.nl/taxonomicon/  | format = Website database  | access-date = 2006-10-13  | archive-date = 2007-09-26  | archive-url = https://web.archive.org/web/20070926212334/http://www.taxonomy.nl/taxonomicon/  }}
* {{cite web|title=David Roos's Seminar: Biology of Apicomplexan Parasites|url=https://www.ibiology.org/microbiology/apicomplexa/}}

{{Life on Earth}}
{{Eukaryota|D.}}
{{Alveolata}}
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{{Authority control}}
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[[Category:Apicomplexa| ]]
[[Category:Alveolata phyla]]
[[Category:Endoparasites]]