The archae and nitrogen fixing bacteria are the sole members of the Kingdom Monera.

Archea:

Like bacteria, they are prokaryotes and do not have true nucleus. They are lived in harsh habitats like as salty areas (halophiles), hot springs (thermoacidophiles) and marshy areas (methanogens). They have different cell wall structure which helps them to survive in extreme conditions. Methanogens are responsible for the production of methane or biogas from sewage treatment and cow dung.

 Nitrogen-fixing bacteria:

Blue-green algae or cyanobacteria  are an example of nitrogen-fixing bacteria. They have chlorophyll like green plants and they are photosynthetic autotrophs. They may be unicellular, colonial or filamentous. The colonies are surrounded by gelatinous sheath. They are characterized by the presence of a rigid cell wall, and if motile, a flagellum. They can also fix atmospheric nitrogen.