Apicomplexans are a group of single-celled organisms belonging to the phylum Apicomplexa. They are primarily known for being parasitic and can infect a variety of hosts, including humans and animals. Notable examples include Plasmodium, which causes malaria, and Toxoplasma gondii, which can lead to toxoplasmosis. These organisms have complex life cycles that often involve multiple hosts. Apicomplexans are characterized by their unique cellular structure, which includes an apical complex that helps them invade host cells. They reproduce through a process called schizogony, where they undergo multiple fission to produce numerous offspring. Understanding apicomplexans is crucial for developing treatments for the diseases they cause.