Lampreys have no jaws. Instead, they have a circular mouth with rows of teeth at the end of their long, eel-like bodies. Their mouths can suction, while the teeth scrape, making them not unlike a vacuum cleaner hose fitted with a stiff brush. Some lampreys feed on other species (parasitize), attaching their mouths to the side of large fishes and scraping up blood or flesh. A hole carved in the side of the host fish, coupled with natural anticoagulants added by the lamprey to keep the blood flowing, the host often dies. The lamprey detaches after several days and finds a new host. Young lampreys are not like vacuum cleaners. They are little, blind larvae that spend years buried in bottom mud where they filter feed. When they change into an adult form, some species become parasitic, attaching to a fish, and others just spawn and die.

Agnathans stand out as the only back-boned animals (vertebrates) that don’t have jaws (agnatha = “no jaws”). Circular mouths with rings of teeth are used to feed and to cling to surfaces (using suction). During development, most vertebrates have a flexible, supportive rod of cells (the notochord) that disappears by adulthood, but is retained in adult jawless fishes. Like sharks, agnathans have a skeleton made of cartilage rather than bone. Having skinny, flexible bodies helps them wiggle their way into small spaces between rocks. They have no fins, other than a small tail fin, and swim by undulating their bodies in a wavelike motion. The two groups of living jawless fishes, lampreys and hagfish, both have an extra “pineal” eye (for hagfish the only working eye). While it cannot see colors, the pineal eye detects light and dark, allowing jawless fishes to find their way into and out of underwater hiding places.