Apicomplexans are a group of single-celled organisms that belong to the phylum Apicomplexa. They are primarily known for being parasitic and can infect a variety of hosts, including humans, animals, and insects. Notable examples include Plasmodium, which causes malaria, and Toxoplasma gondii, which can infect humans and other warm-blooded animals. These organisms have a unique structure called the apical complex, which helps them invade host cells. Apicomplexans reproduce both sexually and asexually, often completing their life cycles in multiple hosts. Their complex life cycles and ability to adapt make them significant in medical and veterinary contexts.