An order of the protozoan subclass Gregarinia, class Telosporea, subphylum Sporozoa. All gregarines are parasites of the digestive tract and body cavity of invertebrates or lower chordates; their mature trophozoites (vegetative stages) live outside the host's cells and are large. The Neogregarinida are thought to be relatively advanced gregarines which live in insects. The most primitive gregarines, the Archigregarinida, differ from the typical gregarines, the Eugregarinida, in having asexual multiple fission (schizogony) before gamonts (cells which will produce gametes) are formed. The Neogregarinida are thought to have acquired this trait secondarily and to have developed from the Eugregarinida.