An animal is a living organism which is usually distinguishable from members of the plant kingdom by its power of locomotion (at least during some stage of its existence).
Animals have a well-defined body shape, limited growth and they feed exclusively on organic matter. Higher forms of animals, such as the vertebrates, are easily distinguishable from plants, but the distinction becomes blurred with the lower forms.
Scientists have classified about a million different kinds of animals in more than twenty phyla. The least evolved or simplest animals include the Protozoa, Sponges, Jellyfish and Worms. Other invertebrate phyla include Arthropods (such as arachnids, crustaceans and insects), Molluscs (shellfish, octopus and squid) and Echinoderms (sea urchins and starfish). Vertebrates belong to the Chordata phylum, which includes fish, amphibians, reptiles, birds and mammals.
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