ceras vs branchia

ceras and branchia both are nouns.

Word	Noun	Adjective	Verb	Adverb
ceras	Yes	No	No	No
branchia	Yes	No	No	No

As nouns, branchia is a hypernym of ceras; that is, branchia is a word with a broader meaning than ceras:

ceras: one of the often brightly colored and branching hornlike structures on the back of the nudibranch (and other related mollusks) that serve as gills
branchia: respiratory organ of aquatic animals that breathe oxygen dissolved in water

Other hypernyms of ceras include gill.

ceras (noun)	branchia (noun)
one of the often brightly colored and branching hornlike structures on the back of the nudibranch (and other related mollusks) that serve as gills	respiratory organ of aquatic animals that breathe oxygen dissolved in water