It might look like a worm but this fish is a fascinating creature that doesn’t get the recognition it deserves. Sure its feeding behaviour might be on the unsavoury side. (Pun intended ;) ) They are part of the “clean up crew” after all, eating the dead carcasses of animals that sink to the ocean bottom, but there is so much more to these guys than meet the eye. Lets start with a fascinating fact about how we humans classify them. Originally they were believed to be the link between vertebrates and invertebrates as they don’t have a vertebral column or spine but they do have the notochord or clump of nerves that extend down the back. They are currently the only known group of animals that have a skull but no spine. Also, even though they have a skull, they have no jaw. Instead their mouth opens sideways and they have a cartilaginous pad that they use to tear away pieces of flesh from the carrion that they eat.
However, being the link between vertebrates and invertebrates wasn’t the main reason these guys have become famous. The real reason is that as a defence mechanism, they turn water into slime. (Cool, they produce a slime, big deal). The slime they produce is one of the softest substances in the world, being about 10 000 to 100 000 times softer than jello. Since its a defence mechanism, they also have to be able to produce it quickly. Hagfish have been known to turn the water in a bucket into slime almost instantly. They way they do this is fascinating. They have glands all down the length of their body, in these glands are cells with proteins that are incredibly tightly wound. When the Hagfish is attacked it releases these cells into the water where they burst and the tightly wound proteins spring out and lengthen, catching on anything in the water from the predator to other proteins which creates the slime. To produce a litre of slime, a Hagfish need only produce 40 mg of dry protein which is about 1000 less dry material than humans need to produce saliva.
Another defence mechanism that the Hagfish has is incredibly loose skin. Its so loose that you add almost 50% of the Hagfish volume and the skin would not stretch yet. What’s more is that the skin only attaches to the body in a few key places. What this means is that when a predator bites or grips the Hagfish, the body is still free to move leaving the predator with a bunch of skin...and slime in its mouth.
For a lot of animals, having these two cool abilities are enough, but not for the Hagfish. Lets talk about how they feed. We have already mentioned that they are part of the clean up crew feeding on dead animals that sink to the depths of the ocean. Depending on the species, Hagfish length can be anything up to about 130cm, or a little over four feet. However, when you are a long tube in water without a jaw, it can be very hard to get enough strength to remove bits of flesh from the carcass to eat. To get around this the Hagfish has developed two great strategies. The first one is that the Hagfish grips a piece of flesh, it then ties its tail into a knot. Since the creature has no bones, it then starts pulling its body through the knot. Eventually the knot sits around the head of the Hagfish and allows the Hagfish to brace itself against the carcass as it pulls the head through the knot and tearing the flesh of the carcass as it does so. The other way the Hagfish can feed is actually by crawling up inside the creature and taking a nap. The Hagfish’ skin is actually more permeable to it’s food than the lining of it’s intestines. This means that it slowly absorbs the...juices (yuck) of the decaying carcass. Its actually more efficient for the Hagfish to eat this way than by tearing off chunks. However, if you tear off chucks and swallow that, then at least you are guaranteed to get the nutrition from that piece. If you just lay and passively absorb the carcass, it can take a while and it leaves the carcass from to be exploited by sharks, crabs and other scavengers.
Either way, these creatures are incredibly fascinating. What is your favourite Hagfish adaptation?