Here's why:

* Prokaryotic: Archaea are single-celled organisms that lack a nucleus and other membrane-bound organelles, making them prokaryotes.

* Cell walls without peptidoglycan: This is a key distinguishing feature of Archaea. Unlike bacteria, which have peptidoglycan in their cell walls, Archaea have diverse cell wall compositions.

While bacteria and archaea were once grouped together as "monera," they are now recognized as separate domains of life due to significant differences in their biochemistry, genetics, and evolution.