Which statement about vertebrate animals is accurate?

Vertebrate animals are defined by their possession of a backbone, which is a key characteristic that distinguishes them from invertebrates. The backbone, or vertebral column, provides structural support and protects the spinal cord, which is crucial for the nervous system and overall bodily function. This structural feature allows vertebrates to exhibit a complex range of movement and adaptability in various environments.

The other statements do not accurately describe vertebrates. For instance, vertebrates do not have external exoskeletons; rather, they typically have an internal skeleton, which can be bony or cartilaginous. Additionally, vertebrates do possess backbones, making the statement about lacking them incorrect. While some vertebrates are warm-blooded, such as mammals and birds, many are cold-blooded, including reptiles, amphibians, and most fish. Therefore, the correct statement emphasizes the defining feature of vertebrates, which is their backbone.