Both manatees and dugongs are part of the same order of Sirenia, but they occupy different families. Manatees are part of the Trichechidae family, while dugongs are part of the Dugongidae family. In more informal terms, this makes them kind of like evolutionary “cousins.”
There are several physical and behavioral differences between them as well. Dugongs occupy marine coastal waters, while manatees are adapted for freshwater areas. They also lack the fluke-like tail of the dugong. The two animals remain similar enough, however, that people may mistake them for each other at first glance.