noun, plural: ookinetes
An ookinete is the motile zygote that forms when the microgamete (derived from the male gametocyte) fertilizes the macrogamete (derived from the female gametocyte) during the sexual reproduction of certain sporozoans such as the malaria-causing Plasmodium.
The life cycle of Plasmodium species is rather complicated in involving two hosts, the Anopheles mosquito and humans. In a human host, there is an exo-erythrocytic cycle and the erythrocytic cycle. The exo-erythrocytic cycle is one in which the species initially invades the liver cell of the human host. The exo-erythrocytic cycle is carried out by the sporozoite form of the species. They particularly invade the vacuole of the hepatocyte where they will go through schizogonic development. Their nucleus will undergo multiple divisions while their cell size increases. They develop and differentiate into merozoites. These merozoites are released from the hepatocytes and enter the bloodstream. They, then, invade the red blood cells to initiate the erythrocytic stage. In the erythrocytic stage, the merozoites may give rise to either trophozoites or gametocytes. The gametocytes may either be male or female type. When they are taken up by a mosquito during a blood meal, these gametocytes differentiate into gametes, i.e. microgamete (male gamete) and macrogamete (female gamete). The microgamete would then fertilize the macrogamete and form an ookinete containing the zygote inside. The ookinete is motile and would penetrate the stomach of the mosquito where it would transform into an oocyst under the outer gut lining of the mosquito.
Word origin: Greek ōon (egg) + kinētos (motile)