decapod vs cephalopod mollusk

decapod and cephalopod mollusk both are nouns.

Word	Noun	Adjective	Verb	Adverb
decapod	Yes	No	No	No
cephalopod mollusk	Yes	No	No	No

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

decapod: cephalopods having eight short tentacles plus two long ones
cephalopod mollusk: marine mollusk characterized by well-developed head and eyes and sucker-bearing tentacles

Other hypernyms of decapod include cephalopod.

decapod (noun)	cephalopod mollusk (noun)
crustaceans characteristically having five pairs of locomotor appendages each joined to a segment of the thorax	marine mollusk characterized by well-developed head and eyes and sucker-bearing tentacles
cephalopods having eight short tentacles plus two long ones