Cyclospora is a genus of microscopic parasites (apicomplexans) best known for Cyclospora cayetanensis, which causes the intestinal illness cyclosporiasis in humans. These parasites are identified by their distinctive oocysts, which contain two sporocysts, each holding two sporozoites. While many species infect mammals like moles, monkeys, and rodents, others are found in reptiles, snakes, and even a millipede, reflecting a remarkably wide host range. Taxonomically, they belong to the coccidia group (family Eimeriidae), but genetic analysis of SSU rRNA suggests they may be more closely related to certain bird-infecting Eimeria species than to other members of that genus. The genus was first described in 1881 from a parasite found in a millipede, marking its long scientific history. This genetic insight highlights that traditional morphology-based classification doesn't always reflect true evolutionary relationships.