A hagfish is an eel-shaped fish that lives in the ocean. Hagfish feed on dead fish and other organisms that live on the seafloor. They have gills like modern fish but have cartilage instead of bones, no jaws and no eyes. Because of these traits, scientists thought that hagfish were “living fossils,” organisms that are similar to animals that lived long before fish evolved bones or scales.
Hagfish are indeed similar to ancient fish, but scientists now know that hagfish are in fact related to modern fish. They evolved bones and eyes long ago — and then lost them. Hagfish didn’t need them for their deep-sea lifestyle. But hagfish did keep a strange method of defense — slime. When attacked, a hagfish can squirt out a liter (or a quart) of slime, making any predator drop the fish in disgust. Scientists have found that hagfish slime is made up of unusually strong, yet lightweight, fibers. Some researchers are exploring how to make similar fibers in the lab. One day, these strong fibers might be used to make helmets, firefighting gear or even shark repellent.