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Apicomplexa

The Apicomplexa (also referred to as Apicomplexia) are a large group of protists, most of which possess a unique organelle called apicoplast and an apical complex structure involved in penetrating a host's cell. They are unicellular, spore-forming, and exclusively^[3] parasites of animals. Motile structures such as flagella or pseudopods are present only in certain gamete stages. This is a diverse group including organisms such as coccidia, gregarines, piroplasms, haemogregarines, andplasmodia. Diseases caused by apicomplexan organisms include, but are not limited to

 http://en.wikipedia.org/wiki/Apicomplexa