What is the criterion for classification of organisms as belonging to kingdom Monera?

The main criterion for classification of organisms as belonging to kingdom monera is 'type of cellular organization’, that is, whether the cell is prokaryotic or eukaryotic.

Prokaryotic cells do not have any double membrane bound structure, like the nucleus, chloroplasts, mitochondria, etc. The ribosomes present are 70s, different from that of eukaryotic cells.