The Apicomplexa are a large group of protists, most of which possess a unique organelle called apicoplast and an apical complex structure invloved in penetrating a host's cell. They're unicellular, spore-forming, and exclusively parasites of animals. Motile structures such as flagella or pseudopods are absent except in certain gamete stages. This's a diverse group including organisms such as coccidia, gregarines, piroplasms, haemogregarines, and plasmodia; some diseases caused by apicomplexan… (More on Apicomplexa)