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The Apicomplexa (also called Apicomplexia) are a large phylum of parasitic protists. Most of them possess a unique form of organelle that comprises a type of plastid called an apicoplast, and an ''apical complex'' structure. The organelle is an adaptation that the apicomplexan applies in penetration of a host cell. The Apicomplexa are unicellular and spore-forming. All species are obligate endoparasites of animals, except ''Nephromyces'', a symbiont in marine animals, originally classified as a chytrid fungus.〔Saffo, M. B., McCoy, A. M., Rieken, C., & Slamovits, C. H. (2010). (Nephromyces, a beneficial apicomplexan symbiont in marine animals ). ''Proceedings of the National Academy of Sciences'', 107(37), 16190-16195.〕 Motile structures such as flagella or pseudopods are present only in certain gamete stages. The Apicomplexa are a diverse group that includes organisms such as the coccidia, gregarines, piroplasms, haemogregarines, and plasmodia. Diseased caused by Apicomplexa include: * Babesiosis (''Babesia'') * Malaria (''Plasmodium'') * Cryptosporidiosis (''Cryptosporidium parvum'') * Cyclosporiasis (''Cyclospora cayetanensis'') * Isosporiasis (''Isospora belli'') * Toxoplasmosis (''Toxoplasma gondii'') The name of the taxon Apicomplexa derives from two Latin words — ''apex'' (top) and ''complexus'' (infolds) — and refers to a 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 the Apicomplexa are motile however, by use of a gliding mechanism that uses adhesions and small static myosin motors. The other main lines were the Ascetosporea (now in Rhizaria), the Myxozoa (now known to be derived from animals), and the Microsporidia (now known to be derived from fungi). Sometimes, the name Sporozoa is taken as a synonym for the Apicomplexa, or occasionally as a subset. ==General features of the Apicomplexa== 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), 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 a mean diameter of about 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. Other morphological findings that are common to all members of this phylum include: *The nucleus is haploid. *Flagella are found only in the motile gamete. These are posteriorly directed and vary in number (usually one to three). *Basal bodies are present. Although hemosporidians and piroplasmids have normal triplets of microtubules in their basal bodies, coccidians and gregarines have nine singlets. *The mitochondria have tubular cristae. *A Golgi apparatus is present. *Centrioles, chloroplasts, ejectile organelles, and inclusions are absent. *Colourless plastids are present in some species. *The cell is surrounded by a pellicle of three membrane layers (the alveolar structure) penetrated by micropores. 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. 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. Most apicomplexans have an apicoplast, (a nonphotosynthetic plastid) and mitochondrial and nuclear genomes, although ''Cryptosporidium'' species and gregarines are possible exceptions, as they are thought to have lost their plastids after the diverging last common ancestor of apicomplexans. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「apicomplexa」の詳細全文を読む スポンサード リンク
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