heterostracan vs jawless fish

heterostracan and jawless fish both are nouns.

Word	Noun	Adjective	Verb	Adverb
heterostracan	Yes	No	No	No
jawless fish	Yes	No	No	No

As nouns, jawless fish is a hypernym of heterostracan; that is, jawless fish is a word with a broader meaning than heterostracan:

heterostracan: extinct jawless fish with the anterior part of the body covered with bony plates; of the Silurian and Devonian
jawless fish: eel-shaped vertebrate without jaws or paired appendages including the cyclostomes and some extinct forms

Other hypernyms of heterostracan include agnathan, jawless vertebrate.

heterostracan (noun)	jawless fish (noun)
extinct jawless fish with the anterior part of the body covered with bony plates; of the Silurian and Devonian	eel-shaped vertebrate without jaws or paired appendages including the cyclostomes and some extinct forms