There are two living types of jawless fish: lampreys and hagfish. Lampreys use their suction cup-like mouths to attach themselves to other fish. Hagfish have long tongues that they use to pull food into their jawless mouths.
Jawless fish fall into the class agnatha, and they are thought to be some of the earliest vertebral species to inhabit the planet. All fish in this class share several characteristics. They do not have paired fins or stomachs, unlike other forms of bony fish. Jawless fish have skeletons made of cartilage and use gill pockets for respiration.
There are approximately 40 living species of lampreys, most of which are parasites in their adult forms. They use their mouths to cling to their prey, piercing a hole in its flesh and slowly sucking out its tissues. There are both marine and freshwater lamprey species.
Hagfish are less developed than lampreys; they lack fully formed skulls. There are more than 40 species of lampreys, all of which live in marine habitats. Hagfish feed on small invertebrates and also scavenge for dead fish. Their mouths contain teeth that they use to tear into the flesh of these dead animals. Hagfish are also known to produce a thick mucous, which makes them slippery and works as a self-defense mechanism against predators.