Trichechus manatus vs sirenian

Trichechus manatus and sirenian both are nouns.

Word	Noun	Adjective	Verb	Adverb
Trichechus manatus	Yes	No	No	No
sirenian	Yes	No	No	No

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

Trichechus manatus: 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 Trichechus manatus include sea cow, sirenian mammal.

Trichechus manatus (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