Animal Kingdom

The animal kingdom is a major group of living organisms that includes all animals. Animals are eukaryotic, multicellular organisms that have specialized tissues and organs, and are capable of movement. There are over 1.5 million known species of animals, ranging from the simplest single-celled organisms to the highly complex and intelligent mammals, such as dolphins and primates. The animal kingdom is divided into several major groups, or phyla, including the chordates (which includes all vertebrates), arthropods (such as insects, spiders, and crustaceans), mollusks (such as snails and octopuses), and many others. Each of these groups is further subdivided into smaller groups based on shared characteristics. Animals play important roles in many ecosystems, including as predators, prey, pollinators, and decomposers. They are also used by humans for food, clothing, medicine, and companionship.