All fish share two traits: they live in water and they have a backbone—they are vertebrates.

Is a jawless vertebrate?

Cyclostomes: Hagfish and Lampreys In fact, they are the only two groups of extant vertebrates that lack jaws.

Do jawless fish have an exoskeleton?

The vertebrate mineralized skeleton is known to have first emerged as an exoskeleton that extensively covered the fossil jawless fish. The evolutionary origin of this exoskeleton has long been attributed to the emergence of the neural crest, but experimental evaluation for this is still poor.