Like other members of Protozoa, Sporozoa do not have structures for locomotion in their mature stages, however, immature forms have some type of movement. All the members of this group are parasites.
The most significant is the genus Plasmodium which causes malaria. They are parasitic and have a very complex life cycle. Part of their life cycle is spent in various vertebrate tissues, and part is innvolves other organisms.
The sporozoite phase of the organism is transferred to a human via the bite of the Anopheles mosquito. The sporozoites enter the bloodstream and migrate to the liver, where they enter the hepatocytes (liver cells) and transform into merozoites.
Merozoites are released from liver cells and infect erythrocytes. While within the erythrocytes, they undergo a process of asexual reproduction that includes some sexual stages. The first is called the ring stage, and the second involves the development of schizonts. When mature, the schizont contains a number of merozoites which are released by lysis of the erythrocyte.
The lysis of the erythrocytes and schizonts at the same time produces the symptoms of malaria (chills, followed by fever, headache, sweating, and malaise).
Released merozoites infect new erythrocytes and repeat the cycle. The cycle of attack is 48-72 hours, depending upon the species.
The sexual phase of the life cycle begins when the merozoites enter the erythrocytes and differentiate into male and female gametocytes. When ingested by the female mosquito during a blood meal, fertilization occurs and the zygote develops into a cyst within the mosquito’s gut wall. After many divisions, the cyst releases, sporozoites, some of which enter the mosquito’s salivary glands ready to be transmitted back to the human.