sirenian
noun
si·re·ni·an sī-ˈrē-nē-ən 
: any of an order (Sirenia) of aquatic herbivorous mammals (such as a manatee, dugong, or Steller's sea cow) that have large forelimbs resembling paddles, no hind limbs, and a flattened tail resembling a fin
sirenian adjective
Did you know?
Sirenian traces back via Latin to Greek seirēn, which is equivalent to our word for the sirens of Greek mythology. And what is the connection between sirens and sirenians? Modern sirenians do not resemble the half bird, half woman creatures who lured sailors to their doom with their sweet singing, but sirenians are considered by some to underlie the ancient legends about mermaids. In European folklore mermaids were sometimes called "sirens," and apparently this confusion resulted in the granting of sirenians the name they bear today.
Example Sentences
Recent Examples on the Web Indeed, the four sirenians in the tank seemed to be eating nonstop during my visit, in between gliding around the tank and coming up for air every few minutes. 
Vanessa Hua, SFChronicle.com, 13 Feb. 2020 Discovered by the German naturalist Georg Steller around the Bering Sea’s Commander Islands in 1741, this enormous and peculiar sirenian became an easy target for Russian hunters. Brian Switek, WIRED, 24 June 2010
Vanessa Hua, SFChronicle.com, 13 Feb. 2020 Discovered by the German naturalist Georg Steller around the Bering Sea’s Commander Islands in 1741, this enormous and peculiar sirenian became an easy target for Russian hunters. Brian Switek, WIRED, 24 June 2010 Word History
Etymology
New Latin Sirenia, from Latin siren
First Known Use
1883, in the meaning defined above