All vertebrates a. endotherms, b. chordates, c. ectotherms, d. echinodermata

All vertebrates are chordates.

Option B

Explanation:

Animal spices corresponding to sub-phylum Vertebrata are chordates with backbones comprises Vertebrates.  

Majority of the phylum chordate represents Vertebrates. Vertebrates comprises of groups like jaw less fishes, jawed vertebrates, tetra pods and bony fishes. Hagfish is traditionally included in the Vertebrates.

Because of the loss in evolution, these have absence of vertebrae. Hagfish has cranium.  Due to this reason, vertebrate sub-phylum is also called Craniata. Vertebral column is the distinct characteristics of vertebrates.  

The notochord presence in chordates that has been replaced with segmented series of stiffer elements. This is separated by mobile joints.

the answer should be a