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.
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.
Gregarinasina