The domain that encompasses unicellular prokaryotes with cell walls lacking peptidoglycan is known as Archaea.
Archaea are a distinct group of microorganisms that share some similarities with bacteria but possess unique biochemical and genetic characteristics. Unlike bacteria, which have cell walls made of peptidoglycan, archaea have cell walls that are often composed of proteins or polysaccharides and can be more resilient to extreme environments. This remarkable adaptability allows many archaea to thrive in harsh conditions, such as extreme temperatures, salinity, or acidity, which are often inhospitable to most other forms of life. Understanding these organisms is critical, as they play essential roles in various ecological processes and can have significant applications in biotechnology.