Tag: hagfish

What, if anything, is a hagfish?

November 22, 2011 • 12:19 pm

by Greg Mayer

Linnaeus thought hagfish were worms, not fish, but there has been considerable controversy about which fish they are closest to. Are hagfish the earliest diverging of all extant vertebrates, or are they closer to lampreys?  The latter hypothesis, which we might call the cyclostome hypothesis (because hagfish and lampreys have been grouped in the taxon Cyclostomata), was favored for many decades. But in the late 20th century, people began to argue that lampreys were closer to jawed fish (gnathostomes), making cyclostomes paraphyletic (i.e. ancestral rather than sister to gnathostomes), which would mean that hagfish were their own group, an early and primitive branch.

In my post, I said recent molecular data had moved us back to the cyclostome hypothesis. Philippe Janvier, one of the most prominent proponents of the paraphyly hypothesis, has come round back to the cyclostome hypothesis, and has an excellent, brief, discussion of the history of the issue and the evidence.  So, hagfish, it seems, are cyclostomes. Money quote:

The results of Heimberg et al. (11) are certainly certainly the most convincing contribution ever published in support of cyclostomes monophyly…, Although I was among the early supporters of vertebrate paraphyly (6, 7), I am impressed by the evidence provided by Heimberg et al. (11) and prepared to admit that cyclostomes are, in fact, monophyletic [i.e. holophyletic].

This is, by the way, an excellent example of how a good scientist accepts new evidence, and alters his views accordingly.

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Janvier, P. 2010. microRNAs revive old views about jawless vertebrate divergence and evolution. Proceedings of the National Academy of Sciences (USA) 107:19137-19138. pdf (may not be open access)

Hagfish, hagfish, hagfish!

November 21, 2011 • 10:24 pm

by Greg Mayer

I’m teaching vertebrate zoology this semester, and one of my favorite topics in the course is the hagfish. Hagfish are jawless, eel-like fish, whose closest relatives are lampreys. (They were once though to be more primitive than lampreys, but molecular data show the two to form a holophyletic group.)  I was thus quite pleased to find that Vincent Zintzen from the Museum of New Zealand and colleagues have a recent paper in Scientific Reports on hagfish defensive and predatory behavior, with accompanying videos.  There’s more at the website of Te Papa Tongarewa (which is the name of the museum in Maori).

Hagfish are well known for producing copious amounts of viscous slime to discourage predators. In the following video, what’s most remarkable to me is how rapidly the hagfish produces sufficient slime to almost instantaneously deter the predators.

Here’s a closeup of slime production from the Vancouver Aquarium:

And here’s a hagfish preying on a burrowing fish. Zintzen et al. suspect the fish has been killed or disabled by choking with slime while in the burrow.

Hagfish are usually thought of as scavengers (notice the cages of dead meat used as bait in the video).  Here’s a more usual feeding episode: large numbers of hagfish gathering on a whale carcass. That sounds like David Attenborough doing the narration.

Finally, here’s an abridged, combined version of the Te Papa videos (if you want to get the under 4 minute version of the whole story):

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Zintzen V., Roberts, C.D., Anderson M.J., Stewart A.L., Struthers C.D. & Harvey E.S. 2011. Hagfish predatory behaviour and slime defence mechanism. Scientific Reports 1: 131, 6 pp. pdf (Scientific Reports is put out online-only by Nature Publishing Group; papers are given at least some peer review, but are not evaluated for how important or interesting they are.)