hermit crab vs decapod

hermit crab and decapod both are nouns.

Word	Noun	Adjective	Verb	Adverb
hermit crab	Yes	No	No	No
decapod	Yes	No	No	No

As nouns, decapod is a hypernym of hermit crab; that is, decapod is a word with a broader meaning than hermit crab:

hermit crab: small soft-bodied marine crustaceans living in cast-off shells of gastropods
decapod: crustaceans characteristically having five pairs of locomotor appendages each joined to a segment of the thorax

Other hypernyms of hermit crab include decapod crustacean.

hermit crab (noun)	decapod (noun)
small soft-bodied marine crustaceans living in cast-off shells of gastropods	crustaceans characteristically having five pairs of locomotor appendages each joined to a segment of the thorax
	cephalopods having eight short tentacles plus two long ones