Chapter 20 Prokaryotic Diversity: Archaea Extremely Halophilic Archaea Methane-Producing Archaea: Methanogenes Hyperthermophilic archaea Thermoplasma: A Cell-Wall-Less archaean Limits of Microbial Existence: Temperature Archaea earliest life forms?Chapter 20 Prokaryotic Diversity: Archaea Extremely Halophilic Archaea Methane-Producing Archaea: Methanogenes Hyperthermophilic Archaea Thermoplasma: A Cell-Wall-Less Archaean Limits of Microbial Existence: Temperature Archaea: Earliest Life Forms?