bubble shell vs gastropod

bubble shell and gastropod both are nouns.

Word	Noun	Adjective	Verb	Adverb
bubble shell	Yes	No	No	No
gastropod	Yes	No	No	No

As nouns, gastropod is a hypernym of bubble shell; that is, gastropod is a word with a broader meaning than bubble shell:

bubble shell: marine gastropod mollusk having a very small thin shell
gastropod: a class of mollusks typically having a one-piece coiled shell and flattened muscular foot with a head bearing stalked eyes

Other hypernyms of bubble shell include univalve.

bubble shell (noun)	gastropod (noun)
marine gastropod mollusk having a very small thin shell	a class of mollusks typically having a one-piece coiled shell and flattened muscular foot with a head bearing stalked eyes