|Pacific hagfish resting on bottom,|
280m down off Oregon coast
Instead of vertically articulating jaws like vertebrates (Gnathostomata), they have a pair of horizontally moving structures with toothlike projections for pulling off food. They enter both living and dead fish, feeding on the insides. Marine worms are also prey. They tend to be quite common in their range, sometimes becoming a nuisance to fisherman by devouring the catch before it can be pulled to the surface.
Hagfish are traditionally included amongst the vertebrates as part of the jawless fish, originally grouped as a class or superclass Agnatha, and in particular were considered closely related to lampreys. This relationship no long appears to be the case, and as they have continuous notochords with no segments they are commonly placed outside the vertebrates proper. The vertebrates and hagfish together make up the craniates.
In recent years hagfish have become of special interest for genetic analysis investigating the relationships among chordates.
About 64 species are known, in 5 genera. A number of the species have only been recently discovered, living at depths of several hundred fathoms.
- Inshore hagfish Eptatretus burgeri
- Black hagfish Eptatretus deani
- Gulf hagfish Eptatretus springeri
- Pacific hagfish Eptatretus stoutii
- Cape hagfish Myxine capensis
- Hagfish (or Atlantic hagfish) Myxine glutinosa
- White-headed hagfish Myxine ios
- J.M. Jørgensen, J.P. Lomholt, R.E. Weber and H. Malte (eds.), The biology of hagfishes (London: Chapman & Hall, 1997)