The backbone is what distinguishes vertebrates from invertebrates
The answer is: The presence of a fragmented and mobile spine.
Vertebrate animals have a backbone, which is the key to distinguishing them from invertebrate animals. This spine provides a strong internal framework for vertebrate animals, which greatly aids their growth and development. Vertebrates also contain a developed skeleton that serves as an internal framework for these animals and helps protect and support them. From this standpoint, it can be said that the spine is what distinguishes vertebrates from invertebrates, and is what makes them able to grow and develop significantly over time.
