Classification
In recent years hagfish have become of special interest for genetic analysis investigating the relationships among chordates. Their classification as agnathans places hagfish as elementary vertebrates in between invertebrates and gnathostomes. However there has been long discussion in scientific literature about whether the hagfish were even non-vertebrate. This position is supported by recent molecular biology analyses which tend to classify hagfish as invertebrates (see references) within subphylum Craniata, because of their molecular evolutionary distance from Vertebrata (sensu stricto). A single fossil of hagfish shows that there has been little evolutionary change in the last 300 million years.
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