Manx cat vs Felis domesticus

Manx cat and Felis domesticus both are nouns.

Word	Noun	Adjective	Verb	Adverb
Manx cat	Yes	No	No	No
Felis domesticus	Yes	No	No	No

As nouns, Felis domesticus is a hypernym of Manx cat; that is, Felis domesticus is a word with a broader meaning than Manx cat:

Manx cat: a short-haired tailless breed of cat believed to originate on the Isle of Man
Felis domesticus: any domesticated member of the genus Felis

Other hypernyms of Manx cat include domestic cat, Felis catus, house cat.

Manx cat (noun)	Felis domesticus (noun)
a short-haired tailless breed of cat believed to originate on the Isle of Man	any domesticated member of the genus Felis