Question

Most _______________ are vertebrates that have a well-defined head and backbone, plus an internal skeleton made up of bone or cartilage.

Answer 1

The answer is Chordates

Chordates belong to the pylum Chordata of the Animal Kingdom.They have the following characteristics;
Lower vertebrates have a notochord which is a hollow nerve chord that is located dorsally of the animal while higher vertebrates have a vertebral column of bone and cartilage. They have a coelom which is a body cavity that differentiates higher vertebrates into organs and digestive tract.