mollusc vs univalve

mollusc and univalve both are nouns.

Word	Noun	Adjective	Verb	Adverb
mollusc	Yes	No	No	No
univalve	Yes	Yes	No	No

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

mollusc: invertebrate having a soft unsegmented body usually enclosed in a shell
univalve: a class of mollusks typically having a one-piece coiled shell and flattened muscular foot with a head bearing stalked eyes

mollusc (noun)	univalve (noun)
invertebrate having a soft unsegmented body usually enclosed in a shell	a class of mollusks typically having a one-piece coiled shell and flattened muscular foot with a head bearing stalked eyes

mollusc (adjective)	univalve (adjective)
	used of mollusks, especially gastropods, as snails etc.