* Vertebrates are animals that have a backbone, also known as a spinal column. This backbone forms the central axis of their internal skeleton. Examples include fish, amphibians, reptiles, birds, and mammals.

The other options are incorrect because:

* Insects have an exoskeleton, which is a hard outer covering.

* Mollusks also have an exoskeleton, usually a shell.

* Cnidarians (like jellyfish and corals) have a simple, fluid-filled body with no internal skeleton.

Let me know if you have any more questions!