Hagfish, (also known as slime eels) the class Myxini (also known as Hyperotreti), are eel-shaped slime-producing fish. They are the only known living animals that have a skull but not a vertebral column. Along with lampreys, hagfish are jawless and are living fossils; hagfish are basal to vertebrates, and have continued to survive into the present day.
Facts[]
The classification of hagfish has been controversial. The issue is whether the hagfish is itself a degenerate type of vertebrate-fish (most closely related to lampreys), or else may represent a stage which precedes the evolution of the vertebral column (as do lancelets). The original scheme groups hagfish and lampreys together as cyclostomes (or historically, Agnatha), as the oldest surviving class of vertebrates alongside gnathostomes (the now-ubiquitous jawed-vertebrates). An alternative scheme proposed that jawed-vertebrates are more closely related to lampreys than to hagfish (i.e., that vertebrates include lampreys but exclude hagfish), and introduces the category craniata to group vertebrates near hagfish. Recent DNA evidence has supported the original scheme.
In Walking with... Series[]
Walking with Dinosaurs[]
Cruel Sea[]
The hagfish were featured in the book version of this chapter as bottom-feeding nocturnal scavengers.
The Complete Guide To Prehistoric Life[]
The hagfish are mentioned in the Haikuichthys and Cephalaspis entries as the modern jawless fish.