Archaediscacea Colaniellacea Earlandiacea Endothyracea Fusulinacea Geinitzinacea Moravamminacea Nodosinellacea Palaeotextulariacea Parathuraminacea Ptychocladiacea Tetrataxacea Tournayellacea The Fusulinida is an extinct order within the Foraminifera in which the tests are traditionally considered to have been composed of microgranular calcite.

However, recent studies based on test microstructure have suggested that fusulinids may be polyphyletic and consist of at least three distinct lineages, and as such are in need of systematic revision.

[1] Traditionally, fusulinid tests were considered to have been composed of very small, tightly-packed calcite crystals with no preferred orientation—a so-called microgranular structure.

a 2017 study using scanning electron microscopy revealed that this supposed structure actually represented tests that had been extensively modified by diagenetic processes.

Members, especially of the Fusulinacea, are excellent index fossils for determining ages and correlating Upper Mississippian to Permian strata.