jellyfish vs Aegina

jellyfish and Aegina both are nouns.

Word	Noun	Adjective	Verb	Adverb
jellyfish	Yes	No	No	No
Aegina	Yes	No	No	No

As nouns, Aegina is a hyponym of jellyfish; that is, Aegina is a word with a more specific, narrower meaning than jellyfish:

jellyfish: any of numerous usually marine and free-swimming coelenterates that constitute the sexually reproductive forms of hydrozoans and scyphozoans
Aegina: small medusa

Other hyponyms of jellyfish include Chrysaora quinquecirrha.

jellyfish (noun)	Aegina (noun)
any of numerous usually marine and free-swimming coelenterates that constitute the sexually reproductive forms of hydrozoans and scyphozoans	small medusa
large siphonophore having a bladderlike float and stinging tentacles	an island in the Aegean Sea in the Saronic Gulf