Six kingdoms of life exist, and animals occupy only one of them. The other eukaryotic kingdoms are Plantae, Protista and Fungi. These four are grouped into the domain Eukaryota, while the other two kingdoms, Archaea and Eubacteria, occupy the domain Prokaryota.
The exact number of kingdoms, and whether kingdom is a valid way of classifying prokaryotes, has been a contentious issue among taxonomists since the 1970s. As of 2014, a consensus of sorts has emerged that life can be divided between prokaryotes and eukaryotes, with one kingdom for each prokaryotic group. Eubacteria are the "true" bacteria, and Archaea is the kingdom of the so-called extremophile organisms that thrive in superhot and supersaline environments. Prokaryotes do not reproduce in linear, hereditary ways, so lower-level classification into phyla or class is extremely difficult. The solution has been simply to describe two kingdoms and group all prokaryotes on one or the other side of the divide.
Among eukaryotes, the lines are more clearly drawn. Regnum Plantae is the kingdom that contains all plant species, and Regnum Fungi contains all species of fungus. Protista are unicellular organisms that are no longer grouped with plants, but have their own kingdom. Finally, Regnum Animalia is the single kingdom reserved to all animals.