Ok, this has to be the most disgusting creature ever. Slime eels (also known as Hagfish) are long, pinkish grey, eyeless eels with no fins. They have a ring of eight tentacles surrounding a toothless mouth. A long projecting tongue is topped with two rasps that are moved against each other to tear off chunks of food. The word which best describes the Slime eel in my mind is "Lovecraftian". I can't look at them without thinking of the Cthulhu myths. A good picture can be found at http://www.mbayaq.org/efc/living_species/default.asp?hOri=1&inhab=198
It only gets grosser however. Not only are these things scary looking, but they have REALLY disgusting habits. If a slime fish is startled, it secretes small packets of sugar and protein into the seawater. The sugar has an affinity for water and turns the entire mix into a mass of gooey slime. Protein strands form in the slime, and give the slime mass its strength and elasticity. One average sized slimefish can produce three GALLONS of slime. Hagfish slime is much more sticky than the slime of other fishes, due to the thousands of microscopic threads of protein woven throughout the mass. The unique properties of this slime have caused it to be the focus of several studies, including one where surgical thread is woven from the protein strands. Indeed, its so sticky that the eel has developed unique ways of clearing itself from the gooey stuff. To clear its nostrils of the slime, a Hagfish will sneeze, something no other fish does. To escape from the cloud of slime, the eel will tie itself into a tight knot, using its own body to scrape the clingy mess from itself.
Gross enough for you? Wait..there's more. Slime eels love to eat liver. Liver is their favorite food, and to get to this treat, the eel will burrow into a dead or dying animal and eat it from the inside out. The eels don't have the necessary teeth for making holes in the body of their victims, so they use the mouth or anus as an entry point. Lovely, huh? For centuries fishermen have hated slime eels for their habit of crawling into netted fish and dining, leaving only an empty bag of bones and fishskin instead of the fat cod that the fisherman had hoped for. Because of this habit, Slime eels are often thought of as scavengers or parasites. But, in fact, most of their diet is made up of marine worms and other invertebrates. So maybe they aren't quite as bad as they seem.
Slime eels are pretty unique reproductively as well. They are born hermaphrodites. Unlike many other fish, the eels undergo direct development, with no larval stage. The newly hatched young are practically miniature versions of their parents. Young are hermaphroditic at first, bearing both sets of sex organs; later in life, they will be either male or female, but may change sex from season to season. They also have an extremely low metabolism. Hagfish eggs are approximately one inch long, and encased in a tough shell. These eggs are large for a fish, and a female can therefore not produce very many. Despite the low number of eggs laid, hagfish exist in large numbers, with populations of up to 15,000 occurring in a relatively small area. This suggests that hagfish have a low mortality rate.
That low mortality rate is partially related to the success of the eel's adaptation to it's environment. Fossil Hagfish from deposits laid down over 300 million years ago are virtually identical to modern specimens. What scientists used to regard as primitive they now consider just a successful body plan and lifestyle! Common belief is that hagfish just haven't needed to change for the last couple of hundred million years.
Slime eels, while once considered only a nuisance and a "trash fish", are now becoming an important fisheries industry. The skins are made into the butter-smooth "eel skin" wallets and belts found in leather stores. Demand has reached the point that they have been largely fished out off Korea and Japan, and over fished on the West Coast of the United States. On the East Coast of the United States, where hagfish harvesting began in 1992, the hagfish catch amounts to more than two and a half tons per year off Massachusetts and Maine, bringing in more than $1 million.
I still think they're gross...and pretty damn cool.