A phylum of parasitic protists (see also protozoa) whose members may have a number of different animal hosts. Their complex life cycle involves the alternation of asexual reproduction (multiple fission) and sexual reproduction and the production of resistant spores (see illustration). The phylum includes the agents causing malaria (Plasmodium) and toxoplasmosis (Toxoplasma). Apicomplexans are now classified as alveolates.