Answer:
Vertebral column.
Step-by-step explanation:
The main division of the animal phylum includes chordates and non -chordates. Most of the chordates have bilateral symmetry, triploblastic animals with the digestive system, circulatory system and excretory system.
Chordates have some specific features that distinguishes them from the non chordates. Chordates posses notochord, dorsal hollow nerve cord, post ana.l tail and pharyngeal gill slits at the specific or the some stages of their life. The vertebral column is present only in vertebrates and not present in other chordates.
Thus, the correct answer is option (c).