Editing Apicomplexa (section)

==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 |pages=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 |pages=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 |pages=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 |doi=10.1093/gbe/evaa244 |url= |publisher=Oxford University Press |pmid=33566096 |pmc=7875001 |issn=1759-6653}}</ref>