A subphylum of Protozoa, typically with spores. The spores are simple and have no polar filaments. There is a single type of nucleus. There are no cilia or flagella except for flagellated microgametes in some groups. In most sporozoa there is an alternation of sexual and asexual stages in the life cycle. In the sexual stage, fertilization is by syngamy, that is, the union of male and female gametes. All sporozoa are parasitic.