gill slit vs body structure

gill slit and body structure both are nouns.

Word	Noun	Adjective	Verb	Adverb
gill slit	Yes	No	No	No
body structure	Yes	No	No	No

As nouns, body structure is a hypernym of gill slit; that is, body structure is a word with a broader meaning than gill slit:

gill slit: one of a series of slit openings in the pharynxes of fishes and aquatic amphibians through which water passes
body structure: a particular complex anatomical part of a living thing and its construction and arrangement

Other hypernyms of gill slit include anatomical structure, bodily structure, complex body part, structure.

gill slit (noun)	body structure (noun)
one of a series of slit openings in the pharynxes of fishes and aquatic amphibians through which water passes	a particular complex anatomical part of a living thing and its construction and arrangement