Which of the following is NOT a shared trait of chordates?

• A. Dorsal hollow nerve cord
• B. Notochord
• C. Pharyngeal gill slits
• D. Lateral line system

Answer: (D)

Chordates are defined by certain features that appear at some point in all members: a dorsal hollow nerve cord, a notochord, pharyngeal gill slits, and a post-anal tail. These traits reflect the basic body plan of the group and are found across diverse chordate lineages. The lateral line system, by contrast, is a sensory structure used to detect water movement and vibration. It is present in many aquatic vertebrates like fishes and some amphibians, but it is not found in all chordates—especially in most terrestrial vertebrates such as birds, reptiles, and mammals. Because it is not universal to all chordates, the lateral line system is not a shared chordate trait.