page_title: Gregarinasina
section_title: Lifecycle
hierarchical_section_title: Gregarinasina / Lifecycle
caption_attribution_description: English: Lankesteria cystodytae, Trophozoite
context_page_description: The gregarines are a group of Apicomplexan alveolates, classified as the Gregarinasina or Gregarinia. The large parasites inhabit the intestines of many invertebrates. They are not found in any vertebrates. However, gregarines are closely related to both Toxoplasma and Plasmodium, which cause toxoplasmosis and malaria, respectively. Both protists use protein complexes similar to those that are formed by the gregarines for gliding motility and invading target cells. This makes them excellent models for studying gliding motility with the goal of developing treatment options for toxoplasmosis and malaria.
  Thousands of different species of gregarines are expected to be found in insects, and 99% of these gregarines still need to be described. Each insect can be the host of multiple species. One of the most studied gregarines is Gregarina garnhami.
  In general, gregarines are regarded as very successful parasites, as their hosts are spread over the entire planet.
context_section_description: Gregarines occur in both aquatic and terrestrial environments. Although they are usually transmitted by the orofaecal route, some are transmitted with the host's gametes during copulation (Monocystis).
  In all species, four or more sporozoites (the precise number depends on the species) equipped with an apical complex escape from the oocysts, a process called excystation, find their way to the appropriate body cavity, and penetrate host cells in their immediate environment. The sporozoites emerge within the host cell, begin to feed, and develop into larger trophozoites. In some species, the sporozoites and trophozoites are capable of asexual replication — a process called schizogony or merogony. Most species, however, appear to lack schizogony in their lifecycles.
  In all species, two mature trophozoites eventually pair up in a process known as syzygy and develop into gamonts. During syzygy, gamont orientation differs between species (side-to-side, head-to-tail). A gametocyst wall forms around each pair of gamonts, which then begin to divide into hundreds of gametes. Zygotes are produced by the fusion of two gametes, and these, in turn, become surrounded by an oocyst wall. Within the oocyst, meiosis occurs, yielding the sporozoites. Hundreds of oocysts accumulate within each gametocyst and these are released via host's faeces or via host death and decay.
  Gregarines have been reported to infect over 3000 invertebrate species.
caption: Lankesteria cystodytae is an intestinal parasite of ascidians. These aseptate gregarines lack epimerites and instead possess attachment organelles known as mucrons
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