These Spine-Chilling Fish Come Equipped with a Secondary Jaw

Moray eels appear frightening enough as they are. Yet, many individuals aren’t aware that these animals possess an additional pair of jaws within their mouth, equipped with pointed teeth. These concealed mandibles only emerge when the carnivorous fish seize food. The PETBOOK editor and zoologist Saskia Schneider elucidates the function of this dual-jaw mechanism.

Initially, you could easily confuse them for eels. Moray eels certainly rank as one of the less recognised predators in the ocean. Nevertheless, numerous Disney enthusiasts will recognise these beings. Within Disney’s "The Little Mermaid," the malevolent sea witch Ursula has two moray eels at her side known as Flotsam and Jetsam (which were renamed Abschaum and Meerschaum in the German dub). These carnivorous fish possess an unsettling appearance; peering out from cracks in rocks with unblinking stares and gaping jaws. It was only in 2007 that scientists found certain species boast a secondary set of jaws positioned further back within their mouth which lurchs forwards during hunting—this feature may bring to mind scenes from the film "Alien." The existence of such dual-jaw systems serves a functional purpose for these aquatic creatures.

What Are Moray Eels?

Moray eels belong to their own clan, called the family Muraenidae. These creatures are snake-shaped bonefish. At present, approximately 200 distinct types have been identified. The majority inhabit warm tropical and subtropical waters close to shorelines. Nonetheless, within European regions, you can find two varieties: the Mediterranean moray (Muraena helena) and the brown moray (Gymnothorax unicolor).

Moray eels do not typically cruise through the open waters of the ocean; instead, they make their homes in coral reefs and along rocky shores. These creatures excel at squeezing into tight spaces due to their slender, serpentine forms. Their ability to fit nearly everywhere often allows just their heads—with those menacingly gaping jaws—to be seen sticking out, adding greatly to their haunting appearance.

What Is the Diet of Moray Eels?

Moro eels are carnivorous fish that subsist solely on meat. These creatures usually hunt after dark, and their diet isn’t limited to particular types of food among the many species. Their preference leans towards certain prey based on whether their teeth are sharp or round. Species equipped with pointed teeth generally go for fish and molluscs such as octopuses, whereas those with blunt teeth favour crustaceans like crabs—though they coexist peacefully with cleaner shrimp through mutualism.

Why They Possess a Dual Jaw

Similar to many predatory fish, moray eels depend on their powerful bites for catching prey. Their robust jaw muscles enable them to exert considerable force when biting. Furthermore, their teeth point inward towards the throat, which stops their catch from wriggling free.

It seems that’s not all; certain types of moray eels possess an additional set of jawbones known as pharyngeal jaws, these too are fitted with keenly pointed teeth. They assist moray eels in consuming their food. This unusual feature came to light back in 2007 when scientists from the University of California, Davis, studied moray eels using X-ray imaging.

They discovered the second set of jaws inside the fish’s throat. These jaws spring into action only after the moray eel has captured a prey item. The pharyngeal jaw then seizes the prey and drags it deeper into the mouth. Once the moray eel has gripped the fish with its own teeth, it does not require additional bites for swallowing; instead, this secondary jaw mechanism takes charge, propelling the meal towards the gullet.

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}

Can Moray Eels Pose a Risk to People?

Moriaeels have an unsettling appearance, and let’s face it: In "The Little Mermaid," Flotsam and Jetsam aren't exactly portrayed as amiable characters. These creatures can instil fear in divers. If they perceive a threat, they will gape their jaws widely and stay like that until the perceived danger subsides. 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 frequently asserted that the Mediterranean moray is among the most toxic types of moray eels globally. This species is one of only a handful discovered in Europe. They inhabit the Atlantic Ocean and can reach lengths of up to 1.4 metres and weights of around 5.5 kilograms. Nonetheless, these creatures do not present any danger—not due to toxicity anyway, since they lack poisonous fangs in their jaws. ^{4 , 5}

Nonetheless, one must avoid provoking them. Despite these predatory fish generally not being hostile towards people, they might strike if they perceive a threat. Often, they will swiftly emerge from their concealment spots and may nip at an individual. Such incidents are not just intensely painful but pose risks beyond mere discomfort—even in the absence of venom. Moray eel bites are particularly hazardous due to the high bacterial content found within their jaws, potentially leading to severe infections following such injuries. ⁶

No wonder these animals have a bad reputation among many divers. Yet, as predators, they play an important role in the marine ecosystem.

1. spektrum.de, “ Raubfisch mit Doppelkiefer ” (accessed of 04.29.2025) ↩︎
2. spektrum.de, “ Shark species have a second set of jaws. ” ( accessed of 04.29.2025 ) ↩︎
3. geo.de, “ Tierlexikon: Muränen – die "Furcht einflößenden Ungeheuer der Ozeane" ” ( accessed of 04.29.2025 ) ↩︎
4. meerwasser-lexikon.de, “ Muränen ” ( accessed of 04.29.2025 ) ↩︎
5. fischlexikon.eu, “ Mittelmeer-Muräne (Muraena helena) ” ( accessed of 04.29.2025 ) ↩︎
6. meeresaquaristik-weber.de, “ The fascinating world of moray eels: A comprehensive insight ” ( accessed of 04.29.2025 ) ↩︎

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