The fish that inspired Ursula’s sidekicks in Disney’s The Little Mermaid are at once odd, majestic, and dangerous.

1. THEY HAVE TWO SETS OF JAWS.

Zina Deretsky, Wikimedia Commons // CC BY 3.0

Like the monster in Alien (1979), morays attack their victims with a hidden set of chompers. Inside the gullet are pair of concealed pharyngeal jaws that help the eel ensnare its prey. Whereas most predatory fish use suction to pull food down their throats, morays instead rely upon a two-step strategy. First, the outer jaws firmly grasp the target. Next, their pharyngeal set shoots forwards, bites the unfortunate victim, and pulls it into the throat.

2. THERE ARE ROUGHLY 200 KNOWN SPECIES.

The family is split into two main divisions: true morays and snake morays. The former are more common by far, with some 166 species presently recognized. Anatomically, their fins represent the biggest difference between these groups—whereas the dorsal fin of a true moray starts just behind its gills, the appendage is limited to the tail region in snake morays.

3. THE BIGGEST ONES CAN WEIGH AT LEAST 66 POUNDS.

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The largest species is the appropriately-named giant moray (Gymnothorax javanicus). So far, the most sizable individuals on record were around 8 feet in length and weighed 66 pounds—but there are unconfirmed reports of monstrous 10-footers swimming around out there. Divers have spotted these animals in the Red Sea, off east African shores, and throughout the Indo-Pacific.

4. SOME HAVE BLUNT TEETH FOR EATING HARD-SHELLED PREY.

The average moray comes with curved teeth that are ideal for snagging fish. Still, a few varieties—like the zebra moray (Gymnomuraena zebra)—dine on crabs, clams, mollusks, and sea urchins. Fare like this requires strong jaws and specialized grinding teeth, so their pearly whites are unusually blunt by moray standards.

5. MOST ARE NOCTURNAL.

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Looking for morays? Take a night swim. By and large, these eels are active after the sun goes down, though a handful—the chain moray, Echidna catenata, for example—have more diurnal lifestyles.    

6. MORAYS WILL SOMETIMES DISLODGE PREY BY TYING THEMSELVES INTO KNOTS. 

When dinner swims down a narrow crevice, how does one retrieve it? Faced with this awkward predicament, the frustrated eel in the above video wraps its tail into a knot. Said knot then travels down the length of its body until it makes contact with the surrounding coral. Once there, the eel pulls with extra force. This technique not only helps morays yank prey out of tight places, but—on occasion—it can be used to rip bite-sized chunks off of large victims.  

7. THE GREEN MORAY (GYMNOTHORAX FUNEBRIS) IS ACTUALLY BROWN. 

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It only looks green because, like many morays, the animal wards off predators by secreting a layer of mucus that covers its skin. This slime contains various toxins, including one which destroys red blood cells. The goo also dramatically changes the fish’s appearance. While green morays are really a drab shade of brown, the gunk’s yellowish tint gives them a more vibrant hue.

8. ONE OF THE MORE OMINOUS LOOKING GESTURES IS TOTALLY INNOCENT. 

While at rest, a moray will slowly open and close its jaws. At first glance, this looks like a “back off” warning to other creatures, but in reality, it’s anything but. Normal fish have bony gill covers on their sides. By constantly opening and shutting these, water is forced over the internal gill chamber, allowing the animal to breathe. Morays have no such covers, so they have to orally pump down H2O in large gulps or die.

9. THE LONG FIN ON THEIR BACKS IS A FUSION OF THREE SMALLER ONES.

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This appendage merges the dorsal, caudal, and anal fins into what appears to be an unbroken single structure.

10. SOMETIMES, GIANT MORAYS JOIN FORCES WITH ANOTHER PREDATOR. 

Whereas the giant moray is a slender and slow-moving ambush hunter, the roving coral grouper (Plectropomus pessuliferus)—with which it shares the Red Sea—is a speedy killer that’s well-suited for long chases in open water. But opposites are wont to attract once in a while.

Every so often, a grouper will invite a moray out onto a joint hunting trip. Upon locating an eel, the carnivore attracts its new partner’s attention with some rapid head-shakes. Each fish complements the other’s talents perfectly: With the moray wriggling through a craggy reef and the grouper hovering overhead, smaller animals have nowhere to hide—and at least one predator gets a meal.