What percentage of all animals are invertebrates?

• A. Vertebrates
• B. Invertebrates
• C. Mammals
• D. Birds

Answer: (B)

The main idea is that most animals lack a backbone. Invertebrates include insects, worms, mollusks, crustaceans, and many other groups, and they make up the vast majority of animal diversity. In fact, about 97% of described animal species are invertebrates, so they represent the lion’s share of all animals. Vertebrates—animals with backbones—are far fewer and include groups like fish, amphibians, reptiles, birds, and mammals. Among those, mammals and birds are just subsets within the vertebrate group, not the majority. So the best answer is the one that refers to invertebrates, because they constitute nearly all animal life.