The backbone (or spinal column) is made up of bones known as the vertebrae and hence the animals that have a backbone are called vertebrates. Some examples of vertebrates are mammals, birds, fishes, reptiles, amphibians, etc. Correspondingly, the animals that do not possess a backbone are called invertebrates. Examples of invertebrates include, worms, spiders, insects, etc. The presence or absence of the backbone is a major classification criteria for organisms. The presence of a backbone enables a vertebrate to be faster and stronger as compared to the invertebrates. Vertebrates are also symmetrical, which means that their left and right sides of their body are the same. Of the known species on planet Earth, over 95% are invertebrates, while the vertebrates make up only (about) 5% of the species.
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