Hagfish

Hagfish is the term for one of a 60 species of very ancient fish that live on sea floors around the world. The oldest fossil Hagfish was discovered in 1991, and is strikingly similar to today's Hagfish, demonstrating that they have changed very little in 300 million years. In fact, Hagfish are so old that they split from the human line over 500 million years ago.

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There is great debate as to whether or not Hagfish are really even fish. Heck, are they even vertebrates? Hagfish have skulls, but no vertebrae. They don't even have jaws. The remainder of the body is made up entirely of cartilage. They have smooth, scaleless bodies, and no fins. Not a whole lot is known about Hagfish reproductive habits, but it is believed that they are born hermaphroditic and settle into a sex as they mature.

Hagfish are blind, though the simple eye that they possess actually is a valuable tool in tracing the evolution of more complex eyes. To make up for their blindness, they have exceptional senses of touch and small. Hagfish are able to search out meals on the dark sea floor using said senses, and these meal often consist of small sea-floor worms. However, Hagfish have a secondary, quite gruesome feeding method. They can attach themselves to dead or injured creatures that are much larger than themselves. They are then able to burrow in to the body of said animal and literally consume it from the inside out.

Another gross thing about Hagfish? The slime. Hagfish secrete a thick mucus from their bodies that serves a a defense mechanism. It is said that a single adult hagfish can secrete up to a gallon of this mucus at a time. The mucus is also full of tiny fibers that make it exceptionally thick and difficult to deal with.