<P> Humans make use of many other animal species for food including meat, milk, and eggs, for materials such as leather and wool, as pets, and as working animals for power and transport . Dogs especially have been used in hunting, while many terrestrial and aquatic animals are hunted for sport . Animals have appeared in art from the earliest times, and feature also in mythology and religion . </P> <P> The word "animal" comes from the Latin animalis, meaning having breath, having soul or living being . The biological definition of the word refers to all members of the kingdom Animalia, whereas in colloquial use, animal often refers to non-human animals . Sometimes the word may refer to only other vertebrates, or just mammals . </P> <P> Animals have several characteristics that set them apart from other living things . Animals are eukaryotic and multicellular, which separates them from prokaryotic bacteria and eukaryotic but unicellular protists . Unlike plants and algae, which produce their own nutrients (and, with fungi, have rigid cell walls), animals are heterotrophic, consuming organic material and digesting it internally . With very few exceptions, animals breathe oxygen and respire aerobically . All animals are motile (able to spontaneously move their bodies) during at least part of their life cycle, but some animals, such as sponges, corals, mussels, and barnacles, later become sessile . The blastula is a stage in embryonic development that is unique to most animals, allowing cells to be differentiated into specialized tissues and organs . </P> <P> All animals are composed of cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins . During development, the animal extracellular matrix forms a relatively flexible framework upon which cells can move about and be reorganized, making the formation of complex structures possible . This may be calcified, forming structures such as shells, bones, and spicules . In contrast, the cells of other multicellular organisms (primarily algae, plants, and fungi) are held in place by cell walls, and so develop by progressive growth . Animal cells uniquely possess the cell junctions called tight junctions, gap junctions, and desmosomes . </P>

List and describe the main characteristics of the kingdom animalia
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