Order Methanococcales

Family Methanocaldococcaceae
Methanocaldococcus - Methanotorris

Family Methanococcaceae
Methanococcus - Methanothermococcus

Class "Methanomicrobia"

Order Methanocellales

Family Methanocellaceae
Methanocella

Order Methanomicrobiales

Family Methanocorpusculaceae
Methanocorpusculum

Family Methanomicrobiaceae
Methanoculleus - Methanofollis - Methanogenium - Methanolacinia - Methanomicrobium - Methanoplanus

Family Methanospirillaceae
Methanospirillum

Unclassified Methanomicrobiales
Methanocalculus - Methanolinea

Order Methanosarcinales

Family Methanosaetaceae
Methanosaeta - Methanothrix

Family Methanosarcinaceae
Halomethanococcus - Methanimicrococcus - Methanococcoides - Methanohalobium - Methanohalophilus - Methanolobus - Methanomethylovorans - Methanosalsum - Methanosarcina

Family Methermicoccaceae
Methermicoccus

Class Methanopyri

Order Methanopyrales

Family Methanopyraceae
Methanopyrus

Class Thermococci or Protoarchaea

Order Thermococcales

Family Thermococcaceae
Palaeococcus - Pyrococcus - Thermococcus

Class Thermoplasmata

Order Thermoplasmatales

Family Ferroplasmaceae
Ferroplasma

Family Picrophilaceae
Picrophilus

Family Thermoplasmataceae
Thermoplasma

Unclassified Thermoplasmatales
Thermogymnomonas