May 1, 2025, 12:59 pm | Read time: 5 minutes
Moray eels already look terrifying on their own. However, few people know that these creatures have a second set of jaws inside their mouths, lined with sharp teeth. This hidden jaw only springs forward when the predatory fish catch prey. PETBOOK editor and biologist Saskia Schneider explains the purpose of this double jaw.
At first glance, you might mistake them for eels. Moray eels are definitely among the lesser-known predatory fish. However, many Disney fans are familiar with these creatures. In Disney’s “The Little Mermaid,” the evil sea witch Ursula is accompanied by two moray eels named Flotsam and Jetsam (in the German re-dubbing also called “Abschaum” and “Meerschaum”). In reality, these predatory fish look quite eerie: with their fixed eyes and open mouths, they peer out from rock crevices. In 2007, researchers discovered that some species have a second jaw hidden deep in their mouths that snaps forward when catching prey. This might remind some of the movie “Alien.” There’s a practical reason why these animals have this so-called double jaw.
What Are Moray Eels?
Moray eels form their own group, the family Muraenidae. They are eel-like bony fish. Currently, about 200 species are known. Most of them live in shallow tropical and subtropical seas. However, there are also two species found in Europe: the Mediterranean moray (Muraena helena) and the brown moray (Gymnothorax unicolor).
Moray eels are not among the fish that swim freely in the sea. They primarily live in coral reefs and rocky cliffs. They have specialized in living in narrow crevices. Thanks to their elongated, snake-like bodies, they can find shelter almost anywhere. Usually, only their heads with open mouths protrude, which significantly contributes to the eerie factor of these fish.
What Do Moray Eels Eat?
Moray eels are predatory fish and feed exclusively on meat. They typically hunt at night, and the various species do not specialize in specific food or prey. Depending on whether they have rounded or pointed teeth, moray eels prefer different prey. Those with pointed teeth mainly target fish and cephalopods like octopuses, while species with rounded teeth prefer hard-shelled prey like crabs — except for cleaner shrimp, with which they live in symbiosis.
Why They Have a Double Jaw
Like most predatory fish, moray eels rely on their bite when hunting prey. They have strong jaw muscles that allow them to bite down hard. Additionally, their teeth are directed backward in the mouth, preventing their prey from escaping.
As if that weren’t enough, some moray eel species have a second set of jawbones, the so-called pharyngeal jaws, which are also equipped with sharp teeth. These help moray eels swallow their prey. This anatomical peculiarity was discovered only in 2007 when researchers at the University of California, Davis, examined moray eels with X-rays.
They found the second pair of jaws in the throat of the fish. It only snaps forward when the moray eel has already caught a prey animal. The pharyngeal jaw grabs the prey and pulls it further back. The moray eel only needs to catch the fish with its teeth and doesn’t need to bite again to swallow it — the second jaw takes over, moving the food toward the esophagus.
Researchers suspect that the double jaw is an adaptation to the moray eels’ specific lifestyle. These predatory fish prefer to lurk in narrow rock crevices for their victims. This makes it difficult for them to snap expansively at their prey. However, the second jaw makes snapping so effective that moray eels don’t need to catch their prey with a perfectly placed bite. It’s enough if they get the fish of their choice between their teeth.1, 2
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Are Moray Eels Dangerous to Humans?
Moray eels look quite eerie, and let’s be honest: In the movie “The Little Mermaid,” Flotsam and Jetsam don’t come across as particularly friendly. They sometimes cause unease among divers. When they feel threatened, they open their mouths wide and remain in this position until the danger has passed.3
Additionally, some species are venomous. Their venom glands are located in the oral mucosa behind the hook-shaped teeth and release venom directly into the wound when they bite. However, there are only a few species whose venom is actually dangerous or even deadly to humans.
It is often claimed that the Mediterranean moray is one of the most venomous moray eels in the world. It is one of the few species found in Europe. These animals live in the Atlantic and can grow up to 1.4 meters long and weigh 5.5 kilograms. However, they pose no threat—at least not from venom, as they do not have venomous teeth in their mouths.4, 5
Nevertheless, they should not be provoked. Even though these predatory fish are not aggressive toward humans, they can attack if they feel threatened. They often dart out of their hiding places and can bite. This is not only very painful but also dangerous even without venom. The mouths of moray eels contain many bacteria, which can cause bite wounds to become severely infected.6
No wonder these animals have a bad reputation among many divers. Yet, as predators, they play an important role in the marine ecosystem.