A lamprey is a primitive, eel-like fish with a circular mouth ringed with sharp teeth. Instead of jaws, a lamprey has a suction-cup mouth that it uses to latch onto other fish. Once attached, it uses its rough tongue to scrape through the host’s skin and feed on blood and body fluids. Picture a living vacuum cleaner with teeth, and you’ll have the right idea.

Lampreys have existed for over 360 million years, making them older than dinosaurs. They’re one of the few surviving jawless fish, a group that dominated ancient oceans long before sharks evolved. Their skeleton is made entirely of cartilage (like a shark’s), and they have a single nostril on top of their head.

While lampreys look frightening, they’re also fascinating to scientists who study evolution. Because they’ve changed so little over millions of years, lampreys offer clues about what early fish were like. Some lamprey species never feed on other animals at all: they hatch in streams, transform into adults, spawn, and die without ever eating as adults.