cyanobacteria vs nostoc

cyanobacteria and nostoc both are nouns.

Word	Noun	Adjective	Verb	Adverb
cyanobacteria	Yes	No	No	No
nostoc	Yes	No	No	No

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

cyanobacteria: predominantly photosynthetic prokaryotic organisms containing a blue pigment in addition to chlorophyll; occur singly or in colonies in diverse habitats; important as phytoplankton
nostoc: found in moist places as rounded jellylike colonies

Other hyponyms of cyanobacteria include trichodesmium.

cyanobacteria (noun)	nostoc (noun)
predominantly photosynthetic prokaryotic organisms containing a blue pigment in addition to chlorophyll; occur singly or in colonies in diverse habitats; important as phytoplankton	found in moist places as rounded jellylike colonies