isopod vs sea louse

isopod and sea louse both are nouns.

Word	Noun	Adjective	Verb	Adverb
isopod	Yes	No	No	No
sea louse	Yes	No	No	No

As nouns, sea louse is a hyponym of isopod; that is, sea louse is a word with a more specific, narrower meaning than isopod:

isopod: any of various small terrestrial or aquatic crustaceans with seven pairs of legs adapted for crawling
sea louse: marine isopod crustacean

Other hyponyms of isopod include slater, wood louse, woodlouse, sea slater.

isopod (noun)	sea louse (noun)
any of various small terrestrial or aquatic crustaceans with seven pairs of legs adapted for crawling	marine isopod crustacean