The chordata phylum includes the well known vertebrates, such as fish, birds, and mammals such as humans. The size of chordates vary to a large degree. Some species in the phylum mature at the size of one cm, whereas the biggest chordate to ever live on this earth is the blue whale, who can grow up to be 30 cm. All chordates have a notochord, which is an elongated, rod-like, skeletal structure dorsal to the gut tube and ventral to the nerve cord.