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The Hagfish - A Strange Animal with a Useful Slime or Mucus
A Living Fossil
The hagfish is a strange sea creature with a very elongated body. It looks something like an eel but belongs to a different group of animals. Hagfish are jawless and are known for the large amount of slime that they produce. They are also famous for feeding on dead and dying animals - often from the inside of these creatures - and scraping the flesh off with their teeth, which are located on a movable cartilaginous plate.
Hagfish are sometimes called "living fossils". They have a partial skull, which is made of cartilage, but they have no vertebrae, so technically they can't be classified as either a vertebrate or a fish. Based on the fossil evidence, their appearance hasn't changed significantly for 300 million years.
Hagfish have one feature that is potentially very useful for humans. Their skin makes a sticky and protective slime that is made of mucus. The mucus contains strong threads made of protein. Researchers hope to use the threads to make a fabric. One species of hagfish is useful for other reasons and is harvested in large numbers. People in some countries like to eat the flesh of this hagfish. The skin is used to make a product that resembles leather and the slime is used in place of egg white in recipes.
Hagfish belong to the phylum Chordata and the class Myxini. They were once classified in the class Agnatha with the lamprey. Like the lamprey, the hagfish contains no jaws.
Pacific Hagfish at Scripps Institution of Oceanography
The Hagfish's Body
Hagfish are sometimes known as "slime eels". They are generally pink, blue-grey, dark brown or black in color. The animals have three or four pairs of tentacle-like structures around their mouths and nostril. These tentacles are called barbels. Hagfish also have a white patch of skin where each eye is located. The eye has no lens and no muscles, but it does have a simple retina containing light receptors. Hagfish can distinguish light from dark but can't see an image.
Hagfish have an excellent sense of smell and a good sense of touch to compensate for their poor vision. They have a single nostril, which is located above their mouth and carries chemicals to the olfactory organ. The barbels contain touch receptors and may play a role in taste sensation as well. The hagfish hears via two inner ears.
The slime glands of a hagfish are visible as a row of white spots on each side of the body. The animals have no scales and have a skeleton made of cartilage. Unlike fish, they have no dorsal fin on their back and no paired fins. They do have a tail or caudal fin, however, which extends along the top and bottom of the animal for a short distance.
Hagfish have four hearts - one main one and three accessory ones. They have a gut but no stomach. They breathe by means of gills. Water enters a hagfish's body through the nostril and travels through the nasal canal to the olfactory organ. It then passes through the nasopharyngeal duct to the gills.
Collecting and Observing Hagfish
How Big is a Hagfish?
An adult hagfish has an average length of about twenty inches. Some species are much longer and some are much shorter, however. The goliath hagfish (Eptatretus goliath) is known from only one specimen discovered off the coast of New Zealand in 2006. The animal was a female and had a length of 4.2 feet. This is the longest hagfish known so far. On the other hand, the dwarf hagfish (Myxine pequenoi) seems to be about 7 inches in length. Its size is based on the two specimens discovered so far, which were obtained off the coast of Chile.
Scavengers at Work
Diet and Feeding Method
Hagfish live in burrows on the muddy sea floor, generally in deep water. Despite their reputation for invading and eating the bodies of larger animals, hagfish eat mainly polychaete worms (relatives of earthworms) and other invertebrates found on the ocean bottom. They are predators as well as scavengers and have been observed entering burrows to catch fish. They are said to be able to go for months without food, however.
Hagfish are often considered a nuisance by fisherman, since when the fishermen haul in their catch they may find that the catch is only skin and bone and has hagfish inside.
A hagfish feeds by a rasping motion, using teeth located on a plate of cartilage known as the dental plate. There are two rows of teeth on each side side of the plate. The teeth are made of keratin, a tough protein found in hooves, horns, nails, hair and the outer layer of our skin. The dental plate acts like a rasping tongue and is both protractable and retractable.
A Hagfish Forming a Knot
Slime and Protective Behaviour
The slime of a hagfish is an excellent tool for defence. Immediately after being touched by a potential predator, a hagfish releases a large amount of slime. The slime expands and forms thick, viscous sheets and strands when it mixes with sea water. The slime repels predators and can block the mouth and gills of predatory fish, suffocating them.
The hagfish exhibits another useful behavior to defend itself against attackers. If a person or a predator picks up a hagfish and the animal can't escape, it twists its body into a knot. The knot begins at the head and progresses towards the tail. The knotting process helps to remove the slime off the surface of the hagfish's body, which is thought to repel the predator. The knotting process may also be useful at other times when a hagfish needs to remove an old slime layer from its skin.
If the slime of a hagfish enters its nostril, the animal sneezes to get rid of it.
Defense and Predation
Not much is known about hagfish reproduction. A hagfish appears to start its life as a hermaphrodite, which means that it has both male and female reproductive organs. When it matures, one of the organs functions and the other doesn't. Research suggests that at least some hagfish can change gender during their lives.
It's thought that hagfish have external fertilization, although this isn't known for certain. Females lay eggs with a tough covering. The eggs have hooked filaments on each end which help them to become attached to objects. There is no larval stage. The eggs hatch into miniature hagfish.
Hagfish Slime or Mucus
People who encounter hagfish often consider the slime to be the most unappealing aspect of the animal. However, scientists see great potential in hagfish slime. They hope to use the protein threads to make a strong fabric. Some Canadian researchers have already harvested slime from hagfish, mixed the slime with water and then spun the stretched fibers like silk.
Researchers have found that the protein threads in the slime of the Atlantic hagfish are 100 times thinner than a human hair and ten times as strong as nylon. They also have the advantage of being made by a "green" process, as opposed to fibres made from petroleum.
Scientists don't plan to hunt or farm hagfish. Instead, they hope to genetically engineer bacteria to make hagfish slime. Some bacteria are proving to be very useful in making substances for humans once they have had the correct gene or genes added to them.
Food Uses of Hagfish
The inshore hagfish of the Northwest Pacific Ocean (Eptatretus burgeri) lives in much shallower water than other hagfish. Its flesh is used as food in Korea. The skin of this hagfish is known as "eel skin" and is used to make items such as belts, accessories and clothing.
Strange or unpleasant as it may sound, the slime of the inshore hagfish is sometimes used as a substitute for egg white in recipes. The slime is said to be obtained by banging a stick on a tank containing a living hagfish.
This hagfish is used so intensively that its population is decreasing and the IUCN (International Union for Conservation of Nature) classifies it as "Near Threatened".
Would you be willing to touch a hagfish?
Hagfish are sometimes considered to be primitive creatures, but their slime has enabled them to be very successful animals. They have existed almost unchanged for millions of years. Their habits may seem disgusting to us, but they are very helpful for the hagfish and have been a wonderful survival mechanism.
Most hagfish live in deep water and are hard to study in their natural environment. There is still a lot to be learned about these fascinating creatures and their very successful lives. The effort to discover more about them should be very worthwhile.
© 2012 Linda Crampton