Definition: Given a scientific passage and an answer, generate a question for the given answer.
Input: Passage: Chordates include vertebrates and invertebrates that have a notochord. Chordates also have a post-anal tail, dorsal hollow nerve cord, and pharyngeal slits. Vertebrate chordates have a backbone, while invertebrate chordates do not. Invertebrate chordates include tunicates and lancelets; both are primitive marine organisms. Answer: backbone
Output:
What do vertebrate chordates possess that invertebrate chordates do not?