It’s been said that we know less about our own oceans than we do some other planets. So perhaps it’s not surprising that we only need to go for a dive to come face to face with “alien” biology.
Of course, no terrestrial life form, no matter how frightful or exotic it may be, is truly “alien”. But evolution, in its many trials and transformations, has molded some very strange forms from the clay of Earth’s long history. Many of these creature features, via their novelty, spark feelings of shock and discomfort in our terrestrial brains.
Moray eels are one of those forms. Morays are a group of more than 200 species of bony fishes that inhabit all of the world’s oceans. Along their evolutionary journey, the many families of eels (of which morays are but one) have gradually slendered and lost their fins, some to a degree that they look more like snakes than fish. It’s a wonderful example of convergent evolution, two only distantly-related organisms meeting the same end result (long and slithery body shapes) independently.
It’s natural to feel a bit unsettled when you first lay eyes upon such pelagic poltergeists and benthic beasts, whether it’s the relatively familiar eel or the spiral of dental terror that is a lamprey’s mouth:
Can I just say NOPE?
Our disquiet makes biological sense. Human neural circuitry evolved in the presence of (and has adapted to recognize) the body forms of terrestrial fauna, so when faced with the incomprehensible biological distortions resulting from eons spent evolving in a wet, dark world quite unlike our own, a little unease is to be expected. We recognize that these aquatic animals are alive, that their bodies have directions we can understand and parts that we can name, but there’s something that’s just… off about ‘em. I came across a Latin term that fits these oddities quite well: ”xenomorph” meaning ”strange shape.”
Xenomorph is also the name given to the deadly parasitoid extraterrestrials from the Alien movies. They, too, reside in that uncanny valley between familiar forms (head/mouth/arms/hands/legs) and extraordinary strangeness, creepy chimeras with skulls but no eyes, familiar bipedal anatomy sheathed in insect-like armor stretched over quasi-mechanic skeletons oozing with acidic blood. Oh, and we can’t forget their second set of jaws, ready to snap through your skull like a toothy bolt pistol.
Yet that second set of jaws is not alien at all. We find it in our friends the moray eels.
Morays possess a second set of retractable chompers called pharyngeal jaws (seen in the GIF up top), which are crucial to how they feed. Many fish have realted crushing structures in their throats, but none are able to extend them to grab prey like the moray. So why do eels have them? We think it’s because they had to make an evolutionary tradeoff.
Most fish gulp down their prey using suction. By very quickly extending their jaws open wide, they create a flow of negative water pressure that they use to slurp prey down their throat:
But to do that, gulping fish need wide, flexible jaws that they can expand blazingly fast. The moray eel family has adapted such a narrow head and body shape that they lost the ability to create that suction motion. So instead, it grew a second mouth!
In 2007, scientists from UC Davis used high-speed cameras to capture moray eels using their second jaws to snag prey. To hunt, the eel waits in its dark coral crevice or murky hollow, eyes unblinking and mouth agape, doing its best impression of scenery while it waits for something edible to float near its mouth. Then, in the blink of an eye, it snaps its forward jaws shut around the prey, extending its second pharyngeal set to pull the food down the throat. What a way to go.
Alien monster designer H.R. Giger, who passed away May 12, maintained his movie monster wasn’t inspired by the moray eel, or any other animal. He said his only goal with the Alien xenomorph was to make something “frightening and horrible.”
He certainly succeeded, and in doing so accomplished some convergent evolution of his own. Two sets of pharyngeal jaws, each unsettling in their own way, blending the familiar with the unfamiliar, keeping one terrifying foot rooted in reality and by resting the other just outside the bounds of what we know. Whether a creature is from outer space or just the shadowy parts of the sea, sometimes they’re just too close for comfort.