Kinds of animals and their habitats

Scientists have identified more than a million kinds of animals and find new ones every year. For convenience they are put into groups. By diet: herbivores eat plants, predators eat other animals, omnivores eat both. By body structure: vertebrates have an inner skeleton and a backbone and fall into five classes — mammals, birds, reptiles, amphibians and fish. Invertebrates have no backbone: insects, arachnids, molluscs, worms, jellyfish, echinoderms. The skeleton protects the inner organs (the skull protects the brain, the ribs protect the heart and lungs), supports the muscles and helps movement. Insects have six legs and a three-part body, while arachnids have eight legs and no antennae.