The apicomplexans are protozoans of the phylum Apicomplexa (also called Sporozoa). They are all parasitic, and thus do not have locomotor appendages, and also lack contractile vacuoles. It has recently been discovered that apicomplexans move (a sliding motion previously attributed to mucus secretion) by minute contractions of very small contractile fibrils. Apicomplexans can live in almost any animal, from a human to another apicomplexan. Some, including the species that cause malaria and coccidiosis, are pathogenic.

Apicomplexan cells are specialized as vertebrate parasites. At the apex of the cell, an apicomplexan contains a complex of organelles designed to penetrate specific host cells and tissue. Apicomplexans feed through one of two processes: saprozoic nutrition, absorbing dissolved nutrients already ingested by the host, of eating the host cell themselves, or fluids of the host organism. The processes of respiration (gas exchange) and excretion of wastes are performed by diffusion directly across the plasma membrane. The apicomplexans can have an alternation of generations in their life cycles. Sexual reproduction usually comes directly before spore production, and asexual reproduction is by binary fission or multiple fission.

Phylum Sporozoa (Apicomplexa)

• Class Gregarinidea
• Class Coccidea
• Class Hematozoea
• Class Perkinsidea