staghorn coral vs stag's-horn coral

staghorn coral and stag's-horn coral both are nouns.

Word	Noun	Adjective	Verb	Adverb
staghorn coral	Yes	No	No	No
stag's-horn coral	Yes	No	No	No

As nouns, staghorn coral and stag's-horn coral are synonyms defined as:

staghorn coral and stag's-horn coral: large branching coral resembling antlers

staghorn coral (noun)	stag's-horn coral (noun)
large branching coral resembling antlers	large branching coral resembling antlers