Any of the multicellular organisms belonging to the kingdom Animalia. All animals are eukaryotes, with each of their cells having a nucleus containing DNA. Most animals develop from a blastula and have a digestive tract, nervous system, the ability to move voluntarily, and specialized sensory organs for recognizing and responding to stimuli in the environment. Animals are heterotrophs, feeding on plants, other animals, or organic matter. The first animals probably evolved from protists and appeared during the Precambrian Era.