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animal
An organism belonging to the kingdom Animalia. Animals are multicellular heterotrophs and generally mobile so that they can seek out food. Specialized sense organs allow them to detect changes in their surroundings, while a nervous system processes information from the senses and enables an appropriate response to be made to environmental stimuli.
Higher animals, such as the vertebrates, are easily distinguishable from plant, but the distinction becomes blurred with the lower orms. Some one-celled organisms could easily be assigned to either catgeory. About a million species of animal have been catgorized in more than 20 phyla. The simplest (least highly evolved) include the protozoa, sponges, jellyfish, and worms. Other invertebrate phyla include arthropods, molluscs, and echinoderms. Vertebrates belong to the chordate phylum, which includes fish, amphibians, reptiles, birds, and mammals.
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• ZOOLOGY
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