Chelonia mydas vs marine turtle

Chelonia mydas and marine turtle both are nouns.

Word	Noun	Adjective	Verb	Adverb
Chelonia mydas	Yes	No	No	No
marine turtle	Yes	No	No	No

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

Chelonia mydas: large tropical turtle with greenish flesh used for turtle soup
marine turtle: any of various large turtles with limbs modified into flippers; widely distributed in warm seas

Other hypernyms of Chelonia mydas include sea turtle.

Chelonia mydas (noun)	marine turtle (noun)
large tropical turtle with greenish flesh used for turtle soup	any of various large turtles with limbs modified into flippers; widely distributed in warm seas