Larus marinus vs sea gull

Larus marinus and sea gull both are nouns.

Word	Noun	Adjective	Verb	Adverb
Larus marinus	Yes	No	No	No
sea gull	Yes	No	No	No

As nouns, sea gull is a hypernym of Larus marinus; that is, sea gull is a word with a broader meaning than Larus marinus:

Larus marinus: white gull having a black back and wings
sea gull: mostly white aquatic bird having long pointed wings and short legs

Other hypernyms of Larus marinus include gull, seagull.

Larus marinus (noun)	sea gull (noun)
white gull having a black back and wings	mostly white aquatic bird having long pointed wings and short legs