HAGFISH DAY: meet the world’s grossest animal (and a living dinosaur)

So ugly it's beautiful? Doubtful for the hagfish, considered to be one of the most disgusting and oldest animals in the world.
So ugly it’s beautiful? Doubtful for the hagfish, considered to be one of the grossest animals in the world.

This third Wednesday in October is Hagfish Day, created to help popularize one of the strangest animals in existence whose other-worldly traits make the species seem more alien than terrestrial. To help celebrate Hagfish Day, we introduce you to what is widely considered to be one of the world’s “most disgusting” animals. Enjoy!


By Mackenzie Englund

From meteor strikes to tectonic collisions, there is no better a place to hide from earth’s catastrophes than at the bottom of the sea. While land dwellers such as the dinosaurs were not so lucky 65 million years ago, ancient species of fish have continued to troll the deep oceans of earth where many species have remained as unchanged as their barren habitats.

Hagfish mouth.
Hagfish mouth.

The unglamorously named hagfish (76 species, nine of which are threatened), part of an ancient lineage of jawless fish known as Agnatha, has prowled the deep for more than 300 million years. Although it possesses no true mouth or bony spine, the hagfish represents one of the most primitive living members of all vertebrates. Its lack of hard skeleton and slime-oozing body give this prehistoric fish an eel-like appearance, earning its nickname as the “slime eel.”

Considered by many experts to be “the most disgusting animal in the world,” the hagfish can go months without food and only feeds on dead or dying animals on the seafloor. With no eyes, no jaw, no bones, no stomach and several hearts (species vary with three, four or five hearts), the hagfish uses four tentacles around its mouth find food.

The most unique aspect that the hagfish is known for is producing an abundance of slime as a defensive move. When a predator or any threat clamps down, the hagfish secretes stringy proteins that turn into a clear, sticky goo when they come into contact with seawater. Though sometimes referred to as a slime eel because of this characteristic, a hagfish is not an eel, but a fish. (There are approximately 100 jawless fish in the Agnatha class, that includes its closest relative, the lamprey.) While legends claim that the hagfish can secrete enough slime in just a few minutes to fill a 5-gallon jug, displays of the animal’s defensive technique prove it does create an ample amount of slime in just seconds.

Lurking in deep seas across the world, from the arctic to the Caribbean, the frilled shark also boasts its prehistoric ancestry with an eel-like architecture. Unlike the hagfish however, and more akin to its current cartilaginous cousins, the frilled shark bears 25 rows of sharp, replaceable teeth. With fossil evidence dating back 95 million years, this shark’s ancestors patrolled the waters while Early Cretaceous tyrannosaurids walked the globe.

Sharing the marine habitat with the frilled shark was the awe-inspiring plesiosaurus, a massive air-breathing marine reptile. It is unlikely that these two competed for food however, as the frilled shark is known to feed mostly on squid, and members of Plesiosauria fed on bony fish in much shallower waters.

So why did plesiosaurs go extinct while frilled sharks and hagfish continued to thrive? The answer exists in differing environments. Much like modern reefs, shallow ocean environments are always in constant flux, with changing temperatures and available amounts of oxygen. This varies greatly from the stillness of the deep ocean, a place of environmental extreme. Cold temperatures at depth mean a slow metabolism for creatures such as the frilled shark. These extreme environments require extreme adaptation, and with the unchanging environment of the deep ocean has come the unchanging of its inhabitants. The hagfish and frilled shark bear these prehistoric traits, and allow scientists to study living forms of ancient animals; as they are creatures of the deep, and of deep time.