A Real Slimeball: Hagfish are long creatures that exude a sticky slime (from which the typical species Myxine glutinosa draws its name). They tie themselves in knots to scrape the slime off of their bodies. Instead of vertically articulating jaws like Gnathostomata (vertebrates with jaws), they have a pair of horizontally moving structures with toothlike projections for pulling off food. Hagfish average about half a metre (18 inches) in length; Eptatretus carlhubbsi is the largest known, with a specimen recorded at 116 cm, while Myxine kuoi and Myxine pequenoi seem to reach no more than 18 cm. An adult hagfish can secrete enough slime to turn a large bucket of water into gel in a matter of minutes.
Uninvited Guests: Hagfish 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 fishermen by devouring the catch before it can be pulled to the surface. When hagfish wish to disengage from their current prey, they form a knot with their body and slide it towards the mouth. The knot provides something to press against in order to pull the mouth off. This is a unique trait. Hagfish are eaten in Japan and South Korea, and their skin is made into "eel leather" in Korea.
Medical Experiments: It has recently been discovered that the mucus excreted by the hagfish is unique in that it includes strong, threadlike fibres similar to spider silk. Research continues into potential uses for this or a similar synthetic gel or of the included fibres. Some possibilities include new biodegradable polymers, space-filling gels, and as a means of stopping blood flow in accident victims and surgery patients.
Life Cycles: Individual hagfish are hermaphroditic, with both ovaries and testes, but the female gonads remain non-functional until the individual has reached a particular stage in the hagfish lifecycle. Hagfish do not have a larval stage, in contrast to lampreys, which have a long larval phase. In recent years hagfish have become of special interest for genetic analysis investigating the relationships among chordates.
There has been long discussion in scientific literature about the hagfish being non-vertebrate. Recent molecular biology analyses however tend to classify hagfish as a vertebrate.
About 64 species are known, in 5 genera. A number of the species have only been recently discovered, living at depths of several hundred metres.
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