beach flea vs amphipod

beach flea and amphipod both are nouns.

Word	Noun	Adjective	Verb	Adverb
beach flea	Yes	No	No	No
amphipod	Yes	No	No	No

As nouns, amphipod is a hypernym of beach flea; that is, amphipod is a word with a broader meaning than beach flea:

beach flea: small amphipod crustaceans that hop like fleas; common on ocean beaches
amphipod: a kind of malacostracan crustacean

beach flea (noun)	amphipod (noun)
small amphipod crustaceans that hop like fleas; common on ocean beaches	a kind of malacostracan crustacean