Apicomplexa

The Apicomplexa (also called Apicomplexia; single: apicomplexan) are organisms of a large phylum of mainly parasitic alveolates. They are a kind of protozoan. Most possess a unique form of organelle structure that comprises a type of non-photosynthetic plastid called an apicoplast—with an 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 endoparasites of animals, except Nephromyces, a symbiont in marine animals, originally classified as a chytrid fungus. 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. 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 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 can use gliding motility, that uses adhesions and small static myosin motors. The other main lines of this obsolete grouping were the Ascetosporea (a group of Rhizaria), the Myxozoa (highly derived cnidarian animals), and the Microsporidia (derived from fungi). Sometimes, the name Sporozoa is taken as a synonym for the Apicomplexa, or occasionally as a subset.