Slime and teeth: Lampreys and hagfish

There are two groups of jawless fishes, and I can’t even decide which one is creepier: the lampreys or hagfishes?

The short version is that lampreys are fish with mouths that don’t have a jaw but rings and rings of teeth. They feed on blood and tissues, which probably loses them quite a few sympathy points for most people. Hagfish are more eel-shaped and fucking slimy. Seriously, whatever slimiest experience you’ve had, it’s probably nothing in comparison.

So, let’s dive in and find out why these creeps are actually pretty fucking cool:

Chapter 1: The lampreys

Remember how we defined fish last time as aquatic vertebrates with gills and fins (and a giant gollop of exceptions-to-the-rule)? Well, the lampreys are one of those exceptions. They lack fins. In general, they are one of the most primitive vertebrates. They don’t even have a spine, because evolution snatched that away.

By Tiit Hunt – Own work, CC BY-SA 3.0,

What they definitely don’t lack is teeth. Fuck, those circles of teeth are weird. There are forty or so species of lampreys alive at this point, and they have very different life cycles and styles. Let’s use the sea lamprey as an example here, because I can’t get into all of those species.

As always, things are pretty complicated, as the sea lamprey is endangered in some of its native range while invasive and thriving in others.

The sea lamprey life cycle sounds exhausting. Sea lampreys spawn in freshwater but live in the sea. They have a pretty long larval stage where they burrow into the river sediment and eat things there for a few years. Then they return to the ocean, live there for a while, before they return to the freshwater. And that’s mostly also where the issues come from.

Sea lampreys are originally from the Atlantic ranging from Labrador to Florida on the Americas side of things and Norway to the Adriatic Sea in Europe. Fish there are ready for them. They have co-evolved to not get chewed to pieces by these things. Ecosystems in balance and all that. But by cutting off access to some of their native spawning grounds, they are struggling.

A study from 2020 looked at their range in Europe where another invasive, the European catfish, is eating a large part of the lamprey offspring. They say, more than half of them get eaten in fewer than 8 days. Isn’t it ironic that the lamprey is invasive elsewhere but suffering in their native range because of an invasive? Okay, they are also suffering because we humans keep building dams, overfish everything, pollute everything, and fuck with their spawning grounds. And then there’s climate change. Okay, I guess I better move on.

The humans fuck with nature part is what also makes them invasive in other places: in the Great Lakes, for example, they got in after the construction of the Welland Canal which bypassed the Niagara Falls. Yay, access. It took a lot of effort by conservation agencies to get a grip on things there. Fish there just weren’t ready for the wounds inflicted by the lampreys and often died. Not good for the fish there–and the connected fisheries that then might leave and overfish elsewhere…

Okay, this is a bit of a downer. Fun fact: In German, and apparently in folklore, these things are called nine-eyed eels or nine-eyes. Well, the German word is Neunauge, which means Nine Eye. The lampreys have seven gill slits on each side, so that’s seven spots that look kinda like eyes. Apparently, the nostril also looks like one. The Japanese don’t seem to count the nostril as an “eye” and their name seems to translate to eight-eyed eel, though I can’t find any reliable source on that one. Still think they’ve got the right idea. The nostrils don’t look like eyes. Even those gill slits are a pretty far stretch. Lampreys do have actual eyes, and the adult ones are rather large. Maybe if they are sleeping? Folklore is weird.

Okay, honestly, that’s all there is to say about the lampreys without getting into boring species differences. Oh, they don’t tend to eat human, by the way. They might accidentally attach themselves to you if you are reaaaaaaally unlucky, but even then, you are way too big for that hole to be a big deal.

Okay, next, slimy madness.

Chapter 2: Hagfishes

Hagfishes don’t have real teeth. They also don’t feed on living things. And they are found in the deep-sea benthos, so the bottom of the ocean. That should make this a lot easier for most of you.

By Justin –, CC BY 2.0,

Hagfishes, the Myxinidae, are scavengers. They eat dead things, making the nutrients available for things with smaller mouths or digestive systems. Or, at least, that’s the norm. Apparently, if you bait them with a fish that can’t swim away, they’ll go for that, too. But somehow, that is still very far from eating living prey in their natural habitat. But time will tell, I guess.

These things look essentially like worms or eels. And what’s really impressive is that they can twist themselves into tight knots and use their body muscles to get out of almost any grip by pushing off on themselves—well, and by being slimy. How slimy they are and how water-soluble that slime is depends on the species.

If you can’t imagine what it looks like to eat without a jaw, I suggest looking at some footage online. There’s a video on the Smithsonian channel with some excellent footage. And, you’ll probably notice those tooth plates that make the whole “no teeth” statement feel like a lie. They aren’t teeth, I promise.

Despite their deep-sea habitat, some of the hagfishes are on the IUCN Red List of Threatened Species. Sad!

Their feeding on things that are dead and rotting away is fucking important for the ecosystems. They are the cleanup crew of the ocean bottom. They make things livable (and also edible) for other species, both smaller and larger than themselves. While you might not give a shit about slimy eel-things, you probably care about cod, haddock, and flounder, as they are popular on the dinner table (and fucking cool animals!).

We’ll get to them in the fishes episodes of the Climbing the Tree of Life series soon. I’m excited!

For now, try to see how cool and important these creatures are. They are more than their teeth–or teeth plates, I guess–and slime. They are an important part of this world’s ecosystems. We need these ugly, slimy, creepy fuckers.



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