The animal kingdom is divided into two groups — vertebrates and invertebrates. The vertebrate group contains all animals with backbones (as well as some that have a primitive form of backbone).Vertebrates include fish, amphibians, reptiles, birds and mammals. Invertebrates have no backbone. They include worms, molluscs, corals, scorpions, spiders, insects and crustaceans such as crabs and lobsters. Scientists divide these two main groups into smaller groupings that show the relationship between all these animals.
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