Family Dugongidae:
* Dugong (Dugong dugon): The only surviving species of the genus *Dugong*. It is found in the Indo-Pacific region and is the only strictly herbivorous marine mammal.
Family Trichechidae (Manatees):
* West Indian Manatee (Trichechus manatus): Found in the Caribbean Sea, the Gulf of Mexico, and the Atlantic coast of South America. It is the largest of the three manatee species.
* Amazonian Manatee (Trichechus inunguis): Found only in the Amazon River basin, this species is the only strictly freshwater manatee.
* African Manatee (Trichechus senegalensis): Found in rivers and coastal areas along the west coast of Africa.
Extinct Sirenians:
Several extinct sirenian species have been discovered, including:
* Steller's Sea Cow (Hydrodamalis gigas): This giant sirenian, which could grow up to 10 meters long, was extinct by the late 18th century due to hunting.
* Metaxytherium: A genus of extinct sirenians that lived from the Oligocene to the Pliocene epochs.
* Prorastomus: A genus of extinct sirenians that lived during the Eocene epoch.
It is important to note that there are several other extinct genera and species of sirenians, highlighting the diversity of this order throughout history.