manatee vs sirenian

manatee and sirenian both are nouns.

Word	Noun	Adjective	Verb	Adverb
manatee	Yes	No	No	No
sirenian	Yes	No	No	No

As nouns, sirenian is a hypernym of manatee; that is, sirenian is a word with a broader meaning than manatee:

manatee: sirenian mammal of tropical coastal waters of America; the flat tail is rounded
sirenian: any of two families of large herbivorous aquatic mammals with paddle-shaped tails and flipper-like forelimbs and no hind limbs

Other hypernyms of manatee include sea cow, sirenian mammal.

manatee (noun)	sirenian (noun)
sirenian mammal of tropical coastal waters of America; the flat tail is rounded	any of two families of large herbivorous aquatic mammals with paddle-shaped tails and flipper-like forelimbs and no hind limbs