Head to head
Hagfish vs Sea Lamprey
Hagfish and lampreys are the last of the jawless fishes, an ancient body plan that predates jaws, paired fins, and bone. Both are long, slimy, and eel-shaped, and both are often lumped together as primitive oddities. But they are not close relatives in the way they look, they feed in completely different ways, and one of them arguably should not be called a vertebrate at all.
| Hagfish | Sea Lamprey | |
|---|---|---|
| Vertebrate? | Not in the strict sense; only a notochord | Yes, with rudimentary vertebral cartilages |
| Jaws | None; two horny toothed plates that pinch | None; a round rasping sucker disc |
| Feeding | Scavenges carcasses; absorbs nutrients through skin | Mostly parasitic on live fish; feeds on blood and fluid |
| Slime | Produces litres of defensive gel almost instantly | Slimy, but no slime-flood defence |
| Eyes | Simple eyespots, poor vision | Well-developed eyes in the adult |
| Life cycle | Direct development; no distinct larva | Years as a blind, burrowing, filter-feeding larva |
| Habitat | Cold sea floor, often deep | Sea and fresh water; breeds in rivers |
| Great Lakes | Not present | A devastating invasive species since the 1900s |
Hagfish vs Lamprey: common questions
Are hagfish and lampreys the same kind of animal?
They are both jawless fishes, and for a long time they were classified together as the "cyclostomes". Modern anatomy suggested they were quite separate, with lampreys closer to jawed vertebrates, but recent genetic work has swung back toward the idea that hagfish and lampreys really are each other's closest relatives, forming a single group that split from everything else with jaws over 500 million years ago. Either way, they diverged from each other so long ago that they now differ enormously in feeding, anatomy, and life cycle.
Is a hagfish a vertebrate?
It depends on the definition. A hagfish has a skull, or at least a partial braincase, but it has no vertebrae; its body is stiffened only by a rod called the notochord, the same structure that a lamprey and even a human embryo start with. Under a strict definition that requires vertebrae, the hagfish is a craniate but not a vertebrate, and lampreys, which have small cartilage elements arching over the nerve cord, just scrape in. This is why textbooks often say "the lamprey is the most primitive living vertebrate" and treat the hagfish as something slightly outside the group.
Why is the sea lamprey a problem in the Great Lakes?
Sea lampreys are native to the Atlantic and naturally enter rivers to breed. Canal building in the nineteenth and early twentieth centuries, particularly improvements to the Welland Canal bypassing Niagara Falls, let them spread into the upper Great Lakes, which had no defences against them. Each parasitic lamprey can kill around 20 kg of fish in its feeding phase, and the population exploded, contributing to the collapse of lake trout and whitefish fisheries by the 1950s. A long-running control programme using barriers, traps, and a lamprey-specific larvicide now holds numbers down, but it has to be maintained indefinitely.