Final answer:
The correct answer is 'b) an open circulatory system' because all vertebrates have a closed circulatory system with a heart, not an open circulatory system.
Step-by-step explanation:
All of these are characteristics of vertebrates except an open circulatory system. Vertebrates are known to have a closed circulatory system with a heart. In a closed circulatory system, the blood is completely contained within blood vessels that carry the blood throughout the body. Vertebrates also exhibit other distinct features:
- A well-developed cranium to protect the brain.
- Paired eyes for vision.
- Pharyngeal slits at some stage of their life cycle, which may develop into gills in fish and amphibians, or contribute to other structures in terrestrial vertebrates.
- A muscular system and an endoskeleton that provide structure and enable movement.
Therefore, the correct answer to the question is 'b) an open circulatory system' as vertebrates have a closed circulatory system, not an open one.