Which of the following is the main characteristic of a vertebrate?

Vertebrates are bilaterally symmetrical, triploblastic, segmented coelomates showing a complex differentiation of body tissues and organs. 

They have a true vertebral column and internal skeleton of bones or cartilage. The vertebral column is commonly known as the backbone and protects the delicate spinal cord. The presence of a backbone or vertebral column is the main characteristic that differentiates vertebrates from invertebrates (lacking a vertebral column).