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Animals can be classified as either vertebrates or invertebrates. Vertebrates, such as mammals and birds, have backbones. These backbones are made of many bones in the animals’ backs. Invertebrates, on the other hand, do not have backbones. In fact, invertebrates do not have any bones. Some invertebrates, such as insects, have hard outer covers on their bodies called exoskeletons. Other invertebrates, such as sponges, have soft bodies.

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