How are all animals categorised as?

All animals are categorized into two primary groups: invertebrates and vertebrates. Invertebrates lack a backbone and include species such as insects, mollusks, and jellyfish. Vertebrates, on the other hand, possess a backbone and are divided into five major classes: mammals, birds, reptiles, amphibians, and fish. Further classification can be made based on various characteristics, including habitat, diet, and reproductive methods.