six-gilled shark vs Hexanchus griseus

six-gilled shark and Hexanchus griseus both are nouns.

Word	Noun	Adjective	Verb	Adverb
six-gilled shark	Yes	No	No	No
Hexanchus griseus	Yes	No	No	No

As nouns, six-gilled shark and Hexanchus griseus are synonyms defined as:

six-gilled shark and Hexanchus griseus: large primitive shark widely distributed in warm seas

Other synonyms of six-gilled shark include cow shark.

six-gilled shark (noun)	Hexanchus griseus (noun)
large primitive shark widely distributed in warm seas	large primitive shark widely distributed in warm seas