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.