It Has No Jaw — Just Rings of Teeth Arranged in a Perfect Circle — and It Uses Them to Bore Through the Side of a Living Fish and Feed for Weeks

360 million years ago, before the first dinosaur walked the earth, before the first flower bloomed, before the continents had finished arranging themselves into anything resembling their current positions, the lamprey existed.

It looked then almost exactly as it looks now.

This is not a metaphor or an approximation. The lamprey is one of the most ancient vertebrates on earth — a jawless, eel-like parasite whose body plan has remained essentially unchanged since the Devonian period, when the most complex life on land was still working out how to breathe air. It survived the Permian extinction that killed 96% of all marine species. It survived the asteroid impact that ended the dinosaurs. It has outlasted every catastrophe that has reshaped life on this planet, and it has done so without evolving a jaw, without developing paired fins, and without acquiring a stomach.

What it has, instead, is a mouth that most people, upon seeing it for the first time, wish they had never seen at all.

The Mouth

There is no gentle way to describe a lamprey’s mouth. It is circular — a perfect ring of cartilage lined with concentric rows of sharp, curved teeth, arranged in a spiral pattern that extends deep into the oral cavity. There is no jaw. There are no lips. There is simply the disc, and the teeth, and behind them a rasping tongue equipped with its own set of cutting structures.

The lamprey uses this apparatus to attach itself to a living fish. It clamps onto the fish’s side — typically targeting the flank or the area behind the gills — and uses its teeth to rasp through the scales and skin. It then secretes an anticoagulant that prevents the wound from clotting, and begins to feed on the blood and body fluids of its host. It may remain attached to a single fish for days or weeks, feeding continuously, before releasing and moving on.

The host fish often survives the initial attack — the lamprey is not trying to kill it, because a dead host stops producing blood. But the wound it leaves is severe, and secondary infections frequently kill the fish after the lamprey has detached. In heavily infested waters, the circular scars left by lamprey attacks are visible on the majority of fish caught by anglers and commercial fishermen.

A Body Built for One Purpose

The lamprey’s anatomy is a study in radical simplification. It has a notochord — a flexible rod of cartilage — rather than a true vertebral column. It has no paired fins, relying instead on a single dorsal fin and its muscular, eel-like body for propulsion. It has no stomach; food passes directly from the oesophagus into the intestine, where digestion occurs. Its circulatory system, its nervous system, its sensory organs — all of them are simpler, more primitive versions of the structures found in jawed vertebrates.

And yet the lamprey is extraordinarily successful. It has survived for 360 million years in a world that has repeatedly and catastrophically reorganised itself. Its simplicity is not a limitation — it is a strategy. A body with fewer complex systems has fewer complex systems that can fail.

The lamprey’s genome, sequenced in 2013, revealed something that surprised researchers: it contains the genetic precursors of the immune system structures found in all jawed vertebrates, including humans. Studying the lamprey’s immune system has provided insights into how the vertebrate immune system evolved — insights that would be impossible to obtain from any other living animal.

The Great Lakes Catastrophe

For most of human history, the sea lamprey (Petromyzon marinus) was confined to the Atlantic Ocean and its connected river systems, where it had coexisted with its prey species for millennia. The fish populations of the Atlantic had evolved alongside the lamprey and had developed some degree of resistance to its attacks. The relationship, while brutal, was ecologically balanced.

Then, in the 1800s, humans began building canals to connect the Great Lakes to the Atlantic seaboard. By the 1930s, sea lampreys had used these canals to enter Lake Ontario, and from there spread progressively through the entire Great Lakes system — the largest group of freshwater lakes on earth, containing 21% of the world’s surface fresh water.

The results were catastrophic. The fish of the Great Lakes — lake trout, whitefish, chub — had never encountered lampreys before. They had no evolved defences. Lamprey populations exploded. By the 1940s and 1950s, lake trout populations in Lakes Huron and Michigan had collapsed almost entirely. The commercial fishing industry, which had been worth hundreds of millions of dollars annually, was devastated.

The response was one of the largest coordinated wildlife management efforts in North American history. A specific lampricide — a chemical toxic to lamprey larvae but relatively harmless to other species — was developed and deployed in lamprey spawning streams across the Great Lakes basin. Barrier dams were constructed to prevent adult lampreys from reaching their spawning grounds. Sterile male lampreys were released to disrupt breeding. The programme has been running continuously since the 1950s and costs approximately $20 million per year to maintain.

It has worked, partially. Lamprey populations in the Great Lakes are now controlled at roughly 10% of their peak levels, and lake trout populations have partially recovered. But the lampreys have not been eliminated — they cannot be — and the management programme must continue indefinitely to prevent a return to the population levels of the 1940s.

What 360 Million Years Looks Like

There is something genuinely humbling about the lamprey. It is not charismatic. It is not beautiful. It does not inspire the kind of conservation sentiment that surrounds elephants or wolves or great apes. It is, by most human aesthetic standards, deeply unpleasant — a parasite with a circular mouth full of teeth, doing something that most people find viscerally disturbing.

But it has been doing that thing, in essentially the same body, since before the first tree grew on land. Every mass extinction, every ice age, every continental shift — the lamprey was there, attaching itself to whatever fish were available, rasping through scales, feeding on blood, and surviving.

It is one of the oldest vertebrates on earth. And the fact that we find it repulsive says considerably more about us than it does about the lamprey.

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Could you bring yourself to eat lamprey? It was considered a royal delicacy in medieval Europe — King Henry I of England allegedly died from eating too many of them. Tell us in the comments!