cephalaspid vs agnathan

cephalaspid and agnathan both are nouns.

Word	Noun	Adjective	Verb	Adverb
cephalaspid	Yes	No	No	No
agnathan	Yes	No	No	No

As nouns, agnathan is a hypernym of cephalaspid; that is, agnathan is a word with a broader meaning than cephalaspid:

cephalaspid: extinct jawless fish of the Devonian with armored head
agnathan: eel-shaped vertebrate without jaws or paired appendages including the cyclostomes and some extinct forms

Other hypernyms of cephalaspid include jawless fish, jawless vertebrate.

cephalaspid (noun)	agnathan (noun)
extinct jawless fish of the Devonian with armored head	eel-shaped vertebrate without jaws or paired appendages including the cyclostomes and some extinct forms