Answer: Phylum
Explanation:
A notochord can be defined as the beginning to the backbone which is primitive. It appears in the embryos as a flexible rod which is made from the germ layer called as mesoderm.
It is one of the 3 layers that is found in the body. These layers are ectoderm, endoderm and mesoderm.
Notochords are only found in the phylum chordata. This phylum belongs a group of animals which includes human.