Answer:The correct answer is chordates
Step-by-step explanation:
Organism in the phylum Chordata develop dorsal nerve cord in their embryonic stage. Development of dorsal nerve cord is the characteristic feature of these animals and is developed by the mesoderm layer. In many of them they are only present in embryonic stage.
In vertebrates notocord disappears after completion of embryonic stage and is replaced by vertebral column which provide support and anchor to the body structure of vertebrates.
Tunicates are chordates and have dorsal nerve cord only in prenatal stage and it disappears in adults.