One kingdom is not named in the graphic. It contains the most ancient bacteria that live in extreme environments. Examples include: halophiles and methanogens. To which kingdom do these belong?

Archaebacteria

Explanation:

Archaebacteria is a group of single cell microbs which possess an ancient form of life. They can be found in some extreme environments such as volcano, hot spring or hot seafloor which is very hot. Some of them can also be found be in a very high salt or a very acidic environment.

The study of Archaea can be very interesting as they reveal how an ancient life work and survive.