What do we call animals that do not possess a backbone?

Animals that do not possess a backbone are classified as invertebrates. This classification encompasses a vast array of organisms, including insects, arachnids, mollusks, and many others. Invertebrates make up approximately 95% of all animal species, highlighting their significant diversity and ecological importance.

The term "vertebrates," on the other hand, refers specifically to animals that do have a backbone, such as mammals, birds, reptiles, amphibians, and fish. Protocords are a more specific group within the animal kingdom related to the early developmental stages of vertebrates and are not a general category for all animals without backbones. Amphibians represent a specific class of vertebrates that typically have a life cycle involving both aquatic and terrestrial stages, hence they also have backbones. In contrast, invertebrates represent a broad and diverse group that does not share this defining characteristic.