Answer:
They have unique ether-linked lipids in their plasma membranes. This is one of the distinguishing features of archaea.
Explanation:
Archaea have an ether linkage between their fatty acids and the glycerol backbone, on other hand the ester linkage seen in bacteria and eukaryotes.
There are two domains of prokaryotes, Archaea and Bacteria. Archaea is prokaryotic( because it doesn't have a nucleus, nor any membrane-bound organelles)but archaeas are not only prokaryotes ,bacteria also belongs in prokaryotes.
The two prokaryote domains, Bacteria and Archaea, split from each other early in the evolution of life. Bacteria are very diverse, ranging from disease-causing pathogens to beneficial photosynthesizers and symbionts. Archaea are also diverse, but none are pathogenic and many live in extreme environments.
