These cells are part of the domains Archaea and Bacteria.

Archaeas and Bacterias are both Prokaryotes. Both used to be classified in Monera kingdom, but later genetists found that they have actually very different genes, despite they both have a similar metabolism. So they think they have a totally different evolutionary origin and they decided to classify them in 2 different domains. The other domain, Eukarya, includes every other organism (all the ones who are not Prokaryots), which are: plants, animals, fungi and protists.