Final answer:
An animal without a backbone is called an invertebrate, which is distinct from vertebrates that have a backbone. Invertebrates encompass a vast majority of animal species, and while invertebrate chordates have a notochord, they do not have a backbone.
Step-by-step explanation:
An animal without a backbone is called an invertebrate. This group includes a vast array of species including insects, earthworms, jellyfish, and many others. Invertebrates are characterized by their lack of a vertebral column, which is the defining feature of vertebrates, another group within the phylum Chordata that includes fish, amphibians, reptiles, birds, and mammals. While all vertebrates are chordates, not all chordates are vertebrates. Some invertebrate chordates, such as tunicates and lancelets, have a notochord but not a backbone.