sertularian vs hydroid

sertularian and hydroid both are nouns.

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

As nouns, hydroid is a hypernym of sertularian; that is, hydroid is a word with a broader meaning than sertularian:

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

Other hypernyms of sertularian include hydrozoan.

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