extremity vs pleopod

extremity and pleopod both are nouns.

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

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

extremity: 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 extremity include chelicera, mouthpart, fang, chela, claw, nipper, pincer, parapodium, fin, swimmeret, limb, dactyl, digit.

extremity (noun)	pleopod (noun)
an external body part that projects from the body	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
that part of a limb that is farthest from the torso
the outermost or farthest region or point
the greatest or utmost degree
an extreme condition or state (especially of adversity or disease)