Explain the phylum chordata?

There are certain characteristic features of the phylum chordata. They have a notochord which is like a solid and stiff rod. It is flexible and is present on the mid dorsal side. It lies between the alimentary canal and central nervous system. It is present permanently in chordates. However in vertebrates it is found in the embryo. In adults, it is replaced by a vertebral column. This is also known as a backbone. They have a central nervous system which is hollow. It is present on the dorsal side of notochord. They have a couple of narrow openings known as the gill slits. They are present on the lateral aspect of pharynx. They also have a tail. It represents a post natal part of the body. It is reduced or absent in adult chordates.