Hagfish are eel-like critters that, at one time, were put in the same group as lampreys. Recently, however, some have suggested that they are the sister group to lampreys (and hence vertebrates. One of the interesting things about hagfish is that they can tie themselves in knots!
Hagfish knots
The also look like what comes out of the Graboids mouth in Tremors (if you haven't seen the Tremors movies you should - there are four of them now)!
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Finally, they produce a lot of slime when nervous!
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The Hagfish Page
Francis Creek Shale Fossils
hagfish.mov
(video/quicktime Object)
Taxonomy of Hagfish