river limpet vs gastropod

river limpet and gastropod both are nouns.

Word	Noun	Adjective	Verb	Adverb
river limpet	Yes	No	No	No
gastropod	Yes	No	No	No

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

river limpet: minute conical gastropod superficially resembling a limpet but living and feeding on freshwater plants
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 river limpet include univalve.

river limpet (noun)	gastropod (noun)
minute conical gastropod superficially resembling a limpet but living and feeding on freshwater plants	a class of mollusks typically having a one-piece coiled shell and flattened muscular foot with a head bearing stalked eyes