The correct answer for the question above is Hagfish.
They have a skull made of cartilage but lack jaws and vertebrae. They swim in a snake-like fashion by using their segmental muscle to exert force against their notochord. They have small eyes, brain, ears, and a nasal opening that connects with its pharynx. They also have tooth formations made of keratin and can tie themselves into a hang knot and also produce slime which allows them to escape humans.
