decapod vs cuttlefish

decapod and cuttlefish both are nouns.

Word	Noun	Adjective	Verb	Adverb
decapod	Yes	No	No	No
cuttlefish	Yes	No	No	No

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

decapod: cephalopods having eight short tentacles plus two long ones
cuttlefish: ten-armed oval-bodied cephalopod with narrow fins as long as the body and a large calcareous internal shell

Other hyponyms of decapod include squid, cuttle, spirula, Spirula peronii.

decapod (noun)	cuttlefish (noun)
crustaceans characteristically having five pairs of locomotor appendages each joined to a segment of the thorax	ten-armed oval-bodied cephalopod with narrow fins as long as the body and a large calcareous internal shell
cephalopods having eight short tentacles plus two long ones