hydrozoan vs hydra

hydrozoan and hydra both are nouns.

Word	Noun	Adjective	Verb	Adverb
hydrozoan	Yes	No	No	No
hydra	Yes	No	No	No

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

Other hyponyms of hydrozoan include planula, siphonophore, sertularian.

hydrozoan (noun)	hydra (noun)
colonial coelenterates having the polyp phase dominant	small tubular solitary freshwater hydrozoan polyp
	trouble that cannot be overcome by a single effort because of its many aspects or its persistent and pervasive quality