Chordata Phylum
Chordata are typically known to have spines (they are vertebrates). The most primitive chordates had no spines, but quickly developed. Chordates are classified into 5 classes: Mammals, Fish, Amphibians, Birds, and Reptiles.
Humans
One example of the respiratory system of chordates is the human. Humans have all the characteristics to fit the phylum of chordata. The respiratory system functions by inhaling air through the nasal or oral cavity led by a tube to the trachea which then sends the oxygen to the lungs. As the lungs use oxygen they turn oxygen into carbon dioxide breathing it out. Humans breathe about 15 - 25 times per minute.
Fish
Fish tend to have a slightly different type of respiratory system. Instead of having lungs they have gills serving as their respiratory organ. Generally, they are found on the side of the fish's head. They intake dissolved oxygen from the aquatic environment they live in, and afterwards convert it into carbon dioxide. They serve the same purpose as lungs, but gills are suitable for an aquatic environment - lungs are not.
Dogs
Dogs have a very similar respiratory system to humans. It works in the same exact way, but is set up in a different shape. The air is breathed in from the nose and/or mouth and is taken to the lungs by the trachea. Because dogs also live in a dry climate, lungs are suitable instead of gills.