Hagfish, sometimes nicknamed "slime eels," are eel-shaped, jawless scavengers that live on the ocean floor. Despite their unglamorous reputation, these ancient creatures are remarkable survivors with one of the strangest defense mechanisms in the animal kingdom.
From their bizarre slime glands to their almost eyeless faces, here are the real facts behind one of the sea's strangest animals.
Hagfish belong to an ancient lineage of jawless fish, with fossils of hagfish-like animals dating back roughly 300 million years to the Carboniferous period.
When threatened, a hagfish can release a thick slime from glands along its body; the slime expands rapidly in water and can clog a predator's gills.
Hagfish have no jaws. Instead, they use a pair of horny, tooth-like plates on a retractable structure to grip and rasp flesh from carcasses.
Hagfish are scavengers that feed on dead or dying marine animals on the seafloor, locating food using a strong sense of smell and touch rather than sight.
Hagfish have a skull made of cartilage but no true vertebrae, only a flexible rod called a notochord running the length of their body.
Hagfish do not have image-forming eyes. Most species have only simple, skin-covered eye spots that can sense light but cannot form pictures.
Hagfish live on or near the seafloor, often in cold, deep water, where they burrow into mud or sediment to hide and rest.
Estimated hagfish lifespans vary a lot by species, with some studies suggesting individuals can live several decades, and Pacific hagfish possibly reaching around 40 years in the wild.
Female hagfish lay a small number of large, yolky eggs, typically ranging from about 1 to 30 depending on the species, which are fertilized outside the body.
Hagfish reproduction is still poorly understood by scientists, since their deep-sea habitat makes it very hard to observe eggs, mating, or early development in the wild.
Overfishing for hagfish meat and skin (sold as "eel skin" leather) has caused population declines in some regions, prompting calls for better fishery management.
A hagfish can tie its own body into an overhand knot and slide the knot along its length, a trick it uses to scrape off excess slime or to brace itself while tearing food.
Scientists have described roughly 80 to 90 living species of hagfish worldwide, found in cold ocean waters on nearly every continent's coastline.
Hagfish slime is made of mucus combined with thousands of coiled protein threads that unravel almost instantly in seawater, turning a small amount of slime into a large, sticky mass.
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