Hagfish (Hyperotreti or Myxini) are jawless fish.
A hagfish has a long body and looks like an eel.
Sometimes, hagfish are known as slime eels because they excrete large quantities of mucus, or slime, when they are threatened.
They are also sometime called blind eels because they are thought to be almost blind.
Although hagfish have skulls, they do not have spinal columns. Therefore, they are not vertebrates.
They are the only animals that have skulls but do not have spinal columns.
Hagfish can be found on ocean floors, on the continental shelves in temperate regions of both the northern and southern hemisphere.
They live in large groups of as many as 15,000 individuals.
Sometimes, they will bury themselves in the muddy ocean bottom, leaving only their heads exposed.
Hagfish have long grayish or pinkish bodies. On average, they are about 1 ½ feet long.
They have no scales.
A hagfish has a tail.
It has a caudal fin (tail fin), but it does not have a dorsal fin (back fin) or paired fins.
The skull of a hagfish is made of cartilage.
A hagfish has eyespots. It is believed that hagfish can use their eyespots to detect light but that hagfish are incapable of recognizing images.
In order to navigate, a hagfish relies on an acute sense of smell.
A hagfish also has four pairs of whisker-like tactile organs (organs of touch) around its mouth. These tactile organs are known as barbels.
Hagfish have four hearts. Each heart pumps blood in a different region of the body.
A hagfish has one nostril. It breathes by taking in water though its nostril and then expelling it through a series of spherical breathing pouches, each of which contains two gills.
The gills of hagfish are simpler than the gills found in jawed fish.
When a hagfish is alarmed, it excretes slime from glands in its skin.
This slime is reinforced with microfibers. The slime expands when it contacts water.
The hagfish will clean the slime off itself by tying itself into a knot. It will allow the knot to pass down the length of its body, wiping the slime off as the knot passes.
This knot-tying process will allow the hagfish to escape from a predator.
Hagfish may excrete slime in order to suffocate predators by clogging their gills.
Hagfish eat small invertebrates, such as marine worms and crustaceans.
They also act as scavengers, feeding on dead and injured fish.
A hagfish may enter the body of a dead or injured fish through the fish's gills, mouth or anus and then feed on the internal organs of its prey from inside the prey's body.
When eating a large fish, a hagfish may tie itself into a knot in order to give itself leverage so that it can tear the flesh off the fish.
Although a hagfish does not have jaw, it can grab onto food by using a serrated tongue that contains two plates with horny teeth. The hagfish can clamp these plates together in order to grab onto its food and then bring the food to its throat.
Hagfish are sometimes considered a nuisance to fisheries because they may try to feed on fish that humans have already caught.
Scientists aren't sure exactly how hagfish reproduce.
Some species of hagfish are hermaphrodites when they are born. Each hagfish has both an ovary (female reproductive organ) and a testicle (male reproductive organ).
As the hagfish grows, either the ovary or the testicle will mature, while the other sex organ remains dormant, so that the hagfish functions as either a male or a female.
The hagfish's sex may change from season to season, depending on the overall sexual makeup of the group to which it belongs.
It's possible that some hagfish remain hermaphrodites and fertilize their own eggs.
A female hagfish will lay between 1 and 30 eggs. A hagfish egg is large, about one inch long, with a large yolk.
There is no evidence that hagfish go through a larval stage. The youngest hagfish that we have seen look like small adults.