The term animal is used to refer to any living organism that falls in the animal kingdom, one of the kingdoms in the six-kingdom system of classification of species (the other kingdoms are plants, bacteria, archaea, fungi and protists). The following attributes collectively separate animals from other living organisms:
|Attribute||Value for animals||Other kingdoms that share (or may share) this attribute value||Kingdoms that don't share this attribute value|
|Cell type||eukaryotic cell||plants, fungi, protists||bacteria, archaea|
|Cell type||does not have a cell wall||some protists (specifically, protozoa)||plants, fungi, bacteria, archaea|
|Cellularity of organism||multicellular organism||plants, fungi||protists, bacteria, archaea|
|Mode of nutrition||heterotrophic organism||some plants, some protists||most plants (including algae), fungi|
|Nature of birth||embryos pass through a blastula stage||none||all other kingdoms|
The cells of animals are called animal cells. These differ in many important respects from the cells of organisms in other kingdoms.