page_title: Hagfish
section_title: Physical characteristics
hierarchical_section_title: Hagfish / Physical characteristics
caption_attribution_description: Two views of the hagfish (Myxine glutinosa) with analytical overlays and disection.
context_page_description: Hagfish, of the class Myxini, are eel-shaped, slime-producing marine fish. They are the only known living animals that have a skull but no vertebral column, although hagfish do have rudimentary vertebrae. Along with lampreys, hagfish are jawless; they are the sister group to jawed vertebrates, and living hagfish remain similar to hagfish from around 300 million years ago.
  The classification of hagfish had been controversial. The issue was whether the hagfish was a degenerate type of vertebrate-fish that through evolution had lost its vertebrae and was most closely related to lampreys, or whether hagfish represent a stage that precedes the evolution of the vertebral column as is the case with lancelets. Recent DNA evidence has supported the original scheme.
  The original scheme groups hagfish and lampreys together as cyclostomes, as the oldest surviving class of vertebrates alongside gnathostomes. The alternative scheme proposed that jawed vertebrates are more closely related to lampreys than to hagfish, and introduces the category craniata to group vertebrates near hagfish.
caption: Two views of the hagfish (Myxini glutinosa) with analytical overlays and dissection, published 1905
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