These are organisms that lack a well-defined nucleus and cell organelles. Hence, they are categorised as prokaryotes. Though these organisms lack multicellular body designs, they show a wide range of diversity based on many other characteristics.
This kingdom comprises of both organisms whose cells have a cell wall and lack a cell wall. The presence and absence of cell wall has very different effects on body design in these organisms rather than multicellular organisms. They comprise of both autotrophic and heterotopic organisms.
Bacteria, mycoplasma and blue-green algae or cyanobacteria 
Monera: Top left - Bacteria; Top right - Blue-green algae; Bottom - Mycoplasma
The kingdom monera is further classified as archaea that includes the bacteria which can live in harsh conditions. These organisms lack a cell wall. As these organisms can live in extreme temperatures, they are also known as extremophiles and are further classified based on their habitats.
Archea: Top left - Thermophiles; Top right - Methanogen; Bottom - Halophytes
Halophiles - These organisms live in extremely salty water.
Thermophiles - These organisms are found in hot springs and volcanoes.
Methanogens - They are found in the guts of animals like cow and sheep. They are involved in the production of methane gas.