hydroid vs sertularian

hydroid and sertularian both are nouns.

Word	Noun	Adjective	Verb	Adverb
hydroid	Yes	No	No	No
sertularian	Yes	No	No	No

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

hydroid: colonial coelenterates having the polyp phase dominant
sertularian: feathery colony of long-branched stems bearing stalkless paired polyps

Other hyponyms of hydroid include planula, hydra, siphonophore.

hydroid (noun)	sertularian (noun)
colonial coelenterates having the polyp phase dominant	feathery colony of long-branched stems bearing stalkless paired polyps