These animals may look like slimy eels, but many experts don't consider them to be fish. In fact, some taxonomists are hesitant to consider them vertebrates, since they are the only living animals that have a skull but not a vertebral column.
One descriptor that is not a misnomer is slimy. In fact, hagfish secrete a gooey slime when handled or threatened, which in the wild helps them to escape from predators.
From an evolutionary point of view, they can be recognized from fossils that date back to 330 million years ago, and they represent a crucial living link between vertebrates and invertebrates.