mouthpart vs gnathopod

mouthpart and gnathopod both are nouns.

Word	Noun	Adjective	Verb	Adverb
mouthpart	Yes	No	No	No
gnathopod	Yes	No	No	No

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

mouthpart: any part of the mouth of an insect or other arthropod especially one adapted to a specific way of feeding
gnathopod: One of a set of three paired appendages on the thorax of a decapod crustacean, located just posterior to the maxillae and used in feeding.

Other hyponyms of mouthpart include maxilliped, maxillary palpus, labial palpus.

mouthpart (noun)	gnathopod (noun)
any part of the mouth of an insect or other arthropod especially one adapted to a specific way of feeding	One of a set of three paired appendages on the thorax of a decapod crustacean, located just posterior to the maxillae and used in feeding.