leatherback vs marine turtle

leatherback and marine turtle both are nouns.

Word	Noun	Adjective	Verb	Adverb
leatherback	Yes	No	No	No
marine turtle	Yes	No	No	No

As nouns, marine turtle is a hypernym of leatherback; that is, marine turtle is a word with a broader meaning than leatherback:

leatherback: wide-ranging marine turtle with flexible leathery carapace; largest living turtle
marine turtle: any of various large turtles with limbs modified into flippers; widely distributed in warm seas

Other hypernyms of leatherback include sea turtle.

leatherback (noun)	marine turtle (noun)
wide-ranging marine turtle with flexible leathery carapace; largest living turtle	any of various large turtles with limbs modified into flippers; widely distributed in warm seas