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) 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. blood-borne genera within the apicomplexa are three suborders of parasites: 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 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 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. taxonomy further information: wikispecies:apicomplexa history the first apicomplexa protozoan 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, 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 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 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, a comprehensive survey of the phylum was completed: in all, 4516 species and 339 genera had been named. they consisted of: class conoidasida subclass gregarinasina 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 hemogregarines, 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. jacques euzéby (1988) jacques euzéby in 1988 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. roberts and janovy (1996) roberts and janovy in 1996 divided the phylum into the following subclasses and suborders (omitting classes and orders): 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) 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 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. 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 a sister taxon to the hematozoa. this genus is found in the renal sac of molgulid ascidian tunicates. evolution further information: alveolate § phylogeny 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 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. myzozoa apicomplexa s.l. squirmida (digyalum, filipodium, platyproteum) chrompodellids/apicomonadea chromerida (chromera, vitrella, piridium) colpodellida (colpodella) voromonadida (alphamonas, voromonas) apicomplexa s.s. gregarines s.l. cryptosporidium gregarines s.s. marosporida aggregatidae (aggregata, merocystis) margolisiella rhytidocystidae (rhytidocystis) coccidiomorphea coccidia hemogregarines coccidia with a single host (eimeria, isospora, cyclospora) cyst-forming coccidia (toxoplasma, sarcocystis, frenkellia) hematozoa piroplasms (babesia, theileria) hemosporidia (plasmodium, leucocytozoon) dinoflagellates & perkinsozoa janouškovec et al 2015 presents a somewhat different phylogeny, supporting the work of others showing multiple events of plastids losing photosynthesis. more importantly this work provides the first phylogenetic evidence that there have also been multiple events of plastids becoming genome-free.