appendage vs pleopod

appendage and pleopod both are nouns.

Word	Noun	Adjective	Verb	Adverb
appendage	Yes	No	No	No
pleopod	Yes	No	No	No

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

appendage: an external body part that projects from the body
pleopod: one of the paired abdominal appendages of certain aquatic crustaceans that function primarily for carrying the eggs in females and are usually adapted for swimming

Other hyponyms of appendage include chelicera, mouthpart, fang, chela, claw, nipper, pincer, parapodium, fin, swimmeret, limb, dactyl, digit.

appendage (noun)	pleopod (noun)
a part that is joined to something larger	one of the paired abdominal appendages of certain aquatic crustaceans that function primarily for carrying the eggs in females and are usually adapted for swimming
an external body part that projects from the body
a natural prolongation or projection from a part of an organism either animal or plant