Editing Apicomplexa (section)

==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 Q|Q123558544|doi-access=free}}</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}}</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/>