A family of anaerobic METHANOSARCINALES whose cells are mesophilic or thermophilic and appear as irregular spheroid bodies or sheathed rods. These methanogens are found in any anaerobic environment including aquatic sediments, anaerobic sewage digesters and gastrointestinal tracts. There are four genera: METHANOSARCINA, Methanolobus, Methanothrix, and Methanococcoides.
