As a part of the A-Z Photographic Glossary of Biological Terms challenge, today it is H for Hemi-Diaphragm, as illustrated by this West Indian Manatee (Trichechus manatus), Crystal Springs, Florida
Manatees replace a large percentage of air in their lungs with each breath and can therefore prolong intervals in between, in some cases more than 20 minutes; in fact, studies have shown that they can renew about 90% of the air in their lungs in a single breath as compared to humans who renew about 10%. Their nostrils close very tightly like a valve while they are underwater and when they surface all that need appear are the nostrils above water for a few seconds to exhale and then take another breath. Both the lungs and the diaphragms of a manatee extend the length of the body cavity and so are oriented in the same horizontal plane as the manatee is in the water.
An unusual anatomical feature is that each lung is in a separate cavity so that instead of one diaphragm like humans, manatees have two separate “hemi-diaphragms!”