Which term describes animals that do not have a backbone?

• A. Invertebrates
• B. Vertebrates
• C. Arthropods
• D. Mollusks

Answer: (A)

The main idea is that backbone presence defines a big animal-group separation: animals without a backbone are called invertebrates. A backbone, or spinal column, is found in vertebrates, so that term describes animals with backbones. Invertebrates cover a huge variety—think insects, spiders, mollusks, and worms. So the correct term for animals that do not have a backbone is invertebrates. Keep in mind that arthropods and mollusks are examples of invertebrates, not the broad label themselves, which is why they aren’t the right general term here.