They have a small opening on their abdomen that takes in air and transports it directly to the lungs.
The external opening of the urethra is called the meatus or urethral meatus.
The major organ involved in external respiration is the lungs. External respiration is the process by which oxygen is taken in from the air and carbon dioxide is eliminated from the body through the lungs.
There is an advantage to a smaller opening which is that it is easier to trap pathogens like fungal spores and bacteria. This is often cited as to why the lungs don't have openings with a shorter pathway that opens in the chest or back. Some pathogens are trapped in saliva or mucus in the throat but most of it is caught by the mucus in the trachea and bronchi.
The glottis opens to the pharynx leading to the lungs.
Nostrils
meatus
Lungs and Gills are both used for external respiration
The external opening is the urethra. Not really. The urethra is the tube that leads from the bladder. The opening is called the urethral opening.
The opening to book lungs is called a stigma. It allows for gas exchange between the respiratory system and the environment.
This is the external opening of the urethra.
Nipples are the external opening of the mammary glands.