All vertebrates are chordates but all chordates are not vertebrates, why?

Step-by-step solution

Chordates are characterized by the presence of rod-like supporting notochord extending throughout the length of the body. Chordates are divided into three sub-phylum, i.e. Urochordates, Cephalocordates and Vertebrates. In the vertebrates, the notochord in adults is replaced by a cartilaginous or bony vertebral column. However, in Urochordates, the notochord is found only in the tail region, while in cephalochordates the notochord extends above the head in adults. Thus, all vertebrates are chordates but all chordate