Hagfish are marine craniates of the class Myxini, also known as Hyperotreti. Myxini is the only class in the clade Craniata that does not also belong to the subphylum Vertebrata.N. A. Campbell and J. B. Reece (2005). Biology Seventh Edition. Benjamin Cummings, San Francisco CA. That is, they are the only animals which have a skull but not a vertebral column. Despite their name, there is some debate about whether they are strictly fish (as there is for lampreys), since they belong to a much more primitive lineage than any other group that is commonly defined fish (Chondrichthyes and Osteichthyes). Their unusual feeding habits and slime-producing capabilities have led members of the scientific and popular media to dub the hagfish as the most "disgusting" of all sea creatures.http://www.uri.edu/news/releases/html/02-0325-01.htmlhttp://www.ntnu.no/gemini/2003-06e/26-27.htm