sea cradle vs shellfish

sea cradle and shellfish both are nouns.

Word	Noun	Adjective	Verb	Adverb
sea cradle	Yes	No	No	No
shellfish	Yes	No	No	No

As nouns, shellfish is a hypernym of sea cradle; that is, shellfish is a word with a broader meaning than sea cradle:

sea cradle: primitive elongated bilaterally symmetrical marine mollusk having a mantle covered with eight calcareous plates
shellfish: invertebrate having a soft unsegmented body usually enclosed in a shell

Other hypernyms of sea cradle include mollusc, mollusk.

sea cradle (noun)	shellfish (noun)
primitive elongated bilaterally symmetrical marine mollusk having a mantle covered with eight calcareous plates	invertebrate having a soft unsegmented body usually enclosed in a shell
	meat of edible aquatic invertebrate with a shell (especially a mollusk or crustacean)