The Apicomplexa are a taxonomic group that possess structures known collectively as an apical complex. Micronemes lie parallel to the rhoptries and often merge with them at the apex of the cell. Rhoptries and micronemes probably are secretory organelles and facilitate penetration into the host cell. The first group of protozoa that will be covered are the amoebae. The amoebae are common protozoa in most free-living situations.
Most species posses both a trophozoite and cyst stages although exceptions occur.
Some species have developed a parasitic mode of existence in various tissues and organs of animals and it is these that we will discuss in the next section.