Meet one remarkable critter, as close to a vertebrate as we can possible get around here, the hagfish!
The theme for LifePhoto this week is slime and what invertebrate could possibly be more slimy that the hagfish? This an interesting creature in its own regard. Sometimes called slime eels, hagfish are certainly not eels. Unlike eels (and all true fish) the hagfish lacks bones, teeth, and jaws. They do have a skull, but it is cartilage instead of bone. Although they are chordates, they have no vertebrae to support the spinal cord. There are 65 identified species of hagfish in the class Myxini. There is still some discussion on where they fit in, but they are now considered to be a sister group to all vertebrates.
Unfortunately, the hagfish catch flack from all sides, even from biological oceanographers! Almost everyone seems to find them disgusting and repulsive. (Could this be construed as more evidence that they are indeed invertebrates?) Yet, they are very cool creatures and important ecologically as part of the cleaning crew. They eat dead fish and animals, usually from the inside out. Hey, and they are edible as well... Hagfish, anyone?
Of course if you are into larval and embryo forms and evolution, the hagfish has a lot to offer, as PZ showed in an awesome post last year.
But the one thing that generally gets hagfish the disgusting label, though I personally think it's damned cool, is the ability to produce vast quantities of slime -- up to 7 litres being produced by an adult in just minutes. The slime comes from glands located in the sides of the hagfish body which secrete mucous and protein threads. Large amounts of seawater are entrained within the matrix of mucous coated threads creating a vast quantity of slime which can distract or possibly suffocate predators.
Classification is for the Pacific Hagfish, featured at the top of the page
- Eptatretus stouti (Lockington, 1878)