Which statement best defines invertebrates?

Which statement best defines invertebrates?

• A. Animals that lack a backbone or internal skeleton
• B. Animals that have a backbone
• C. Animals with external skeleton
• D. Animals that are insects

Answer: (A)

Invertebrates are animals that do not have a backbone. The statement is the best answer because the defining feature of this group is the absence of a vertebral column, which includes a vast diversity like jellyfish, snails, worms, insects, and starfish. Some invertebrates have external skeletons (insects and crustaceans) or internal skeletons (echinoderms), but the common thread is that they lack a backbone. In contrast, animals with backbones are vertebrates, such as mammals, birds, reptiles, amphibians, and fish. The other options describe only parts of the picture—having a backbone defines vertebrates, an external skeleton covers only a subset, and insects are just one small group within invertebrates.

Invertebrates are animals that do not have a backbone. The statement is the best answer because the defining feature of this group is the absence of a vertebral column, which includes a vast diversity like jellyfish, snails, worms, insects, and starfish. Some invertebrates have external skeletons (insects and crustaceans) or internal skeletons (echinoderms), but the common thread is that they lack a backbone. In contrast, animals with backbones are vertebrates, such as mammals, birds, reptiles, amphibians, and fish. The other options describe only parts of the picture—having a backbone defines vertebrates, an external skeleton covers only a subset, and insects are just one small group within invertebrates.