Few mythical creatures have undergone as many regular and diverse transformations as the modern mermaid. While their mythological backgrounds are just as mercurial as their physical forms – from Hans Christian Anderson’s mermaid, who was unable to cry because she had no immortal soul, to Disney’s Pirates of the Caribbean: On Stranger Tides, in which a mermaid tear grants access to the Fountain of Youth and thus immortality itself – the physical body is quickly catching up to how science might imagine a real mermaid.

The mermaid is a creature that is long overdue for a return to the drawing board. Human women with rainbow-colored goldfish tails, shell tops, and tiaras might have done well in The Little Mermaid in 1989, but slap a CGI version of the same on the live action Ariel character in Once Upon A Time in 2013 and you’ll find you’re in for a tepid response.

Suspension of disbelief can go a long way in an audience, but monofins and neoprene aren’t enough to create a creature that could believably live in the sea. For that, you need scales, a complete re-working of the human/fish muscular and skeletal structures, gills, and more scales, and that’s just to start.

When SFF Gets Mermaids (Mostly) Right…

Harry Potter and the Goblet of Fire actually created mermaids very well. While still noticeably humanoid up top and fish down below, the merfolk created for the movie are alien and predatory creatures that look, and act, as though they belong in their aquatic environment.  Their hair is comprised of scaly ropes more similar to snakes and tentacles than our own keratin-based hair, which is made brittle and will begin to break off if exposed too long to water. Their skin is also noticeably scaly, which continues across the body and is not localized only to their tail– human skin erupts in sores and will eventually become infected or even peel away if constantly submerged in water. Their golden-green coloring allows for better camouflage in their environment, while their teeth are pointed and thin like a barracuda’s – good for trapping and shredding prey.

Most importantly, and often unrecognized, is the way Harry Potter‘s merfolk move.

Generally, mermaids swim by moving their tails up and down, in the same undulating wave-like pattern common amongst whales, dolphins, and other mammals. Aquatic mammals are descended from four-legged land animals and they still share the same spine, which flexes up and down. Human spines flex in the same manner, while human hips severely limit all but forward and backward movement.

Fish do not move in the same way at all.

More closely related to reptiles like snakes and lizards, fish sweep their tails back and forth in order to create forward movement, gliding rather than undulating. It’s a particularly successful evolution in sharks, allowing predators to close in quickly with their often more nimble but less speedy prey. The merfolk in Harry Potter sweep their tails side to side, making them more predatory and less mammalesque, while the long row of abdominal muscles down their front (up to a dozen per creature) still allows them to pivot and assume the upright posture appropriate to their human forequarters.

Perfecting Mermaid Anatomy…

While Harry Potter‘s mermaids set the standard for accuracy, scientifically speaking they’re still not quite there. There’s little use for arms or hands in open water, and marine biologists have also suggested that a mermaid’s nostrils would be at the apex of the head while their back would be ridged with at least one dorsal fin.

As aesthetically unpleasant as the resulting mental image might be, other versions of mermaids have begun to incorporate dorsal fins, noticeably the Siren series, new this year.

Siren‘s take on the mermaid places dorsal fins on the back of the tail, although not the upper human back, and also includes scaled skin throughout, fang-like teeth, webbed hands, and most intriguingly, webbed armpits. The mermaids still move their tails up and down, underlining their mammalian roots and making them a tad less predatory, but their efficiency as carnivores is nevertheless underscored throughout the show, adopting common aquatic hunting techniques like ramming their prey and trying to push them farther down in the water to drown them.

No matter how many different iterations of the mermaid we see in the future, the demand for pretty, pin-up mermaids will still prompt creations like Korea’s Legend of the Blue Sea, which as late as 2016 still gave us a dewy-skinned, doe-eyed mermaid with flowing human hair and a very modest, thick layer of scales over the breasts and nearly up to the shoulders, blending seamlessly into a neoprene tail.

But dangerous, predatory, fish-like mermaids are now on the table, hunting aquatic prey and humans alike.

Hollywood is finally dipping a toe into the bloodier, gorier current of mermaid lore.

Grace Horman

Grace Horman has a degree in history, is currently studying archaeology, and has always had a deep and abiding love for science fiction and fantasy. When not writing, reading, or researching, she tries to catch up on all the TV shows she’s behind on (all of them except ‘Game of Thrones’) and fantasizes about living in their worlds (most of them except ‘Game of Thrones’). She lives in the UK across the street from a library and could ask for nothing more.