invertebrate

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invertebrate Term for an animal without a backbone. There are more than one million species of invertebrates, divided into 30 major groups. One of these is Arthropoda (joint-legged animals), the largest of all animal phyla in terms of numbers of species. Most are insects, but it also includes crustaceans and arachnids. Molluscs make up the second largest group of invertebrates. See also arthropod; crustacean; phylum

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