The Mermaid

The depths of the ocean conceal a myriad of secrets. There is no region of the Earth so unexplored, no biome so little understood. For those species who dwell on the land, the mysteries of the sea have existed as little more than shadows passing beneath its surface. But sometimes, the lines between the domains of land and sea become blurred, and in the image of the mermaid, they have even become fused together.
Over the last thousand years, both the siren and the mermaid have become interchangeable, and the reason is understandable. Both are icons of the sea, both represent beauty… and danger.
As I have already shared, the siren is a different kind of beast than the legends tell. The mermaid, or, merfolk, if you like, is as well, but not for the reasons one might expect.
In fact, when I set out to find the truth behind these famed and allegedly mythical beings, I had little idea what to expect–particularly after my findings in the case of sirenus horridus.
What follows here, my valued listener, are the complete findings my team and I dredged out of those ocean depths… and as with so many creatures once relegated to myth, the truth of the mermaid borders on the unbelievable.

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A few short months before our investigation began, murmurs of a humanoid creature with the tail of a fish were received, coming from the caribbean island of Hispaniola. These, of course, were not the first sightings in the region, nor will they likely be the last, but these reports carried a certain crediibilty that I simply could not ignore.
And so, entirely unsure of what we may find, my team and I were funded and dispatched, landing in a classified location in nearly record time.
After weeks of fruitless searching, interviewing locals, and long, seasick days spent at sea, I was on the verge of losing hope.
But then, as I’m sure comes as no surprise, my colleagues and I at last found fortune. A trap, of sorts, submerged at depth just east of the Windward passage, was triggered.
In truth, I thought it likely to be a common aquatic species, entirely known to science. When the bars of that cage broke through the water as we hauled it up, it took a long moment for what I saw to register in my mind.
What scrambled there was neither fish nor human… it was alien, and yet, somehow, familar. It was a species unlike anything I had seen, and I have dubbed it “aquasapiens pisciformis.”

Evolution

It is the current belief among mainstream scientists that at some point in the distant past, a certain group of artiodactyl progenitors took to the water. Fossils from transition species such as Pakicetus and Ambulocetus appear to exhibit intermediate anatomical adaptations to a semi-aquatic lifestyle, though they still possessed four limbs, and were fully able to walk on land.
Evenutally, protocetid descendants of these species, such as Rodhocetus, refined these aquatic adaptations even further, using their webbed feet for propulsion and their tail as a rudder.
Then came early cetations like basilisaurus, in which the hindlimbs became vistigial, and the forelimbs became flippers. Even more impressively, the spine elongated greatly and now terminated in a primitive fluke, allowing for powerful movement through the water.
Now, we see nearly 100 species of whale, each exhibiting a host of specialized adaptations to a variety of climates, food sources, and even preferred position in the water column.
Should it come as a surprise, my valued listener, that another, unrelated lineage might have followed a similar evolutionary trajectory?
I posit that Aquasapiens pisciformis is descended from a group of shoreline-dwelling primates–much like the group that likely came into contact with Sirenus horridus, along the mediterranean.
Whether due to competition or scarcity elsewhere, this hominid population moved from the trees and took to the abundant resources the shallows provided.
Some of my contemporaries, including a marine biologist by the name of Alister Hardy, have argued that this shoreline–dwelling population became increasingly adapted to the water–including a loss of fur to better facilitate swimming, trading it for layer of insulating subcutaneous fat. Some even view bipedalism as a natural result of this semi-aquatic lifestyle. After all, the versatility of a vertical gait provides many advantages–not only for walking, but also wading and swimming.
This so-called “Aquatic Ape Hypothesis” posits that this lineage eventually gave rise to homo sapiens, and that even our modern physiology echoes our semi-aquatic ancestry. Among the evidences for this theory, perhaps the most intriguing is that of the “diving reflex”–a physiological response that optimizes oxygen conservation, and is initiated when the face is submerged, and water fills the nostrils. Sensory receptors sensitive to wetness within the nasal cavity and areas of the face supplied by the trigeminal nerve relay this information to the brain, which in turn “triggers” the autonomic nervous system. This causes bradycardia, or lowered heart rate, and peripheral vasoconstriction, which restricts blood flow to the limbs and organs, therby preserving blood and oxygen for vital organs such as the heart and brain. This conservation of oxygen allows for a concentration of blood flow in a heart-brain circuit during apnea and facial cooling, both of which serve as triggers for the diving reflex.
Interestingly, children have a higher survival rate than adults when deprived of oxygen underwater, potentially due to a brain cooling mechanism akin to the protective effects observed in individuals treated with deep hypothermia.
The cardiovascular responses associated with the diving reflex are modulated by chemoreceptors in the carotid bodies, which sense changes in blood oxygen, carbon dioxide, and acidity levels during sustained breath-holding. These chemoreceptors relay this information to brain centers responsible for regulating neural outputs to the heart and circulation.
Of course, the diving reflex is also observable in aquatic mammals such as otters, seals, and dolphins, but it is the fact that it exists in humans that should not be ignored.
It is my belief that, at some point, this shoreline-dwelling homind population fractured–one lineage possibly giving rise to humans, which returned to the land. The other lineage, however, would remain in the sea, venturing further and deeper… until they no longer needed to rely on the shore at all.

Anatomy and Physiology

Unlike sirens, merfolk are indeed mammals, and as, I believe, they share a common ancestor with humans, may even be very loosely considered hominids. However, the level of specialization and potentially speciation exhibited by these creatures is more than enough to place them in their own genus.

Lungs

In similar fashion to whales, dolphins, and other marine mammals, merfolk are obligate air breathers, and must surface periodically to inhale oxygen and exhale carbon dioxide.
This may come as a surprise to anyone who might have expected these creatures to have a set of gills, but given pisciformis ancestry, the retention of lungs is not unusual.
There are a number of more derived features, however, that are exhibited in merfolk physiology.
For one, I have observed larger lung capacities, as well as a high concentration of hemoglobin in the bloodstream and elevated myoglobin in the muscle tissue–both of which allow for greater efficiency of retaining oxygen, and increased functionality when oxygen levels are low.
Additionally, we do observe the physiological effects of the same diving reflex present in other aquatic mammals, as well as ourselves: bradycardia and peripheral vasoconstriction when diving, which conserves oxygen for the brain and other vital organs.

Lastly, within the lungs, I have observed an adaptation that serves to resist the higher pressure experienced in deeper dives: abundant respiratory surfactant. This surfactant, a complex mixture of lipids and proteins, is crucial for reducing surface tension at the air-liquid interface within the alveoli, the tiny air sacs wherein gas exchange occurs. Under the high pressure of deep dives, this surfactant prevents the alveoli from collapsing–an undesirable condition known as atelectasis. Indeed, without it, the lungs would be at risk of significant structural compromise during deep dives, leading to decreased efficiency of gas exchange upon resurfacing and inhaling.
Of course, after leaving the shoreline, this lineage underwent a many, many more changes in order to optimize their body structure for swimming. Bones in the hindlimbs, such as the femur, tibia, and fibula were reduced, while various associated muscles such as the biceps femoris, semimembranosus, and gastrocnemius disappeared altogether.

Meanwhile, the vertebrae became greatly elongated–an adaptation especially pronounced in the lumbar and caudal regions, where increased flexibility allowed for powerful undulating movements.
Personal observation of modern merfolk indicates not only more robust vertebrae than, for example, humans, but also, of course, a greatly increased overall number. I have also noted highly derived interverebral discs, which appear to feature radially oriented collagen fibers within the annulus fibrosus, as opposed to the lamellar structure found in terrestrial discs. This radial alignment likely serves to increase the disc's resistance to hoop stresses encountered during swimming movements.
Additionally, the endplates, which connect the intervertebral discs to the adjacent vertebral bodies, seem exhibit specialized fibrocartilaginous properties, creating a smoother transition between the disc and vertebral body. This both enhances load distribution and prevents excessive concentrations of stress.
Of course, for most terrestrial vertebrates, hominids included, the spine isn’t nearly as flexible as what we observe in aquasapiens pisciformis–this is especially true in the lumbar, sacral, and coccygeal regions. This lack of mobility is by design, as they must bear the weight of the upper body and provide stability during weight-bearing activities such as standing, walking, and lifting.
For an aquatic species to swim effectively, however, this had to change. In modern specimens, I have observed great elasticity in certain lumbar intervertebral ligaments, specifically in the supraspinous ligament, the interspinous ligament, and the ligamenta flava. This, paired with horizontally-positioned vertebral facet joints, allows for increased flexibility, while the specialized discs serve to efficiently transfer energy along the entire vertebral column.
But all of this would be much less effective without a more powerful means of propulsion. And so, eventually, at the distal end of the elongating spine, it seems that a rigid, horizontally-oriented wedge of connective tissue began to form, significantly enhancing thrust, and eventually becoming a powerful, hydrodynamic fluke, as the terminal caudal vertebrae became modified to support it.
The adaptation of this “tail” is in stark contrast to that of the siren, which, due to a lack of horizontally-oriented anatomy, exhibits a more anguilliform-style pattern of locomotion.

Indeed, merfolk swim with wave-like movements along the body's dorsoventral axis, in a pattern known as dorsoventral oscillation. In terms of locomotion, when compared to the siren, this gives pisciformis the distinct advantage of greater efficiency and endurance, and enables it to move through the water at speeds of up to 14 miles per hour.
Interestingly, although the lumbar and caudal vertebrae proliferated and elongated, forming the tail, the cervical vertebrae, or the bones in the neck, appear to have shortened, resulting in less flexibilty. This loss of articulation has a major benefit, however, as it likely provides greatly increased head stability when swimming near top speed.
After abandoning bipedalism entirely, and in order to support this entirely new method of movement, the musculature surrounding the spine also underwent extensive changes. Epaxial muscles such as the longissimus and iliocostalis began to extend along the entire length of the spinal column, while the hypaxial muscles, such as the rectus abdominis and the obliques, also increased in size.
And although my time did not allow for in-depth analysis in this area, it does appear that this enhanced musculature exhibits altered innervation and a proliferation of proprioceptors, which likely provide feedback on tail position, muscle tension, and movement.
Finally, the pelvis, which once supported the hindlimbs and facilitated a vertical gait also underwent a gradual reduction in both size and function.
In fact, in my observations of modern merfolk specimens, it appears that the pelvis is no longer directly connected to the vertebral column nor the hindlimbs at all, and other than serving as limited support for various smaller muscles, it has become, essentially, a vestigial structure.

Hands and Arms

But unlike the hindlimbs, the forelimbs were retained. The reason for this is clear: among the progenitor homind population, tool use was likely already widepread. This, of course, gave this lineage a distinct advantage in terms of resource gathering, as well as defense from predators.
Even as this splinter group moved into the water, the advantages provided by articulate forelimbs likely proved invaluable.
Still, a number of adaptations do appear to have occured here. First, certain bones of the wrist, including the scaphoid, lunate, and triquetrum bones have partially fused, significantly reducing mobility between them. Additionally, the extensor retinaculum, a thick band of connective tissue on the back of the wrist, apepars more taut than that of a human, further restricting wrist mobility. As a result, muscles like the pronator teres, responsible for rotating the forearm and hand in humans, is greatly reduced.
Overall, this reduction in mobility allows for much improved transfer of energy while treading water, while still allowing enough articulation for grasping and hunting movements.
Further adaptations include elongation of the phalanges, as well as elastic, interphalangeal skin membranes. Interestingly, some would argue that because of a common descent from a semi-aquatic ancestor, humans exhibit vestigial webbing between the fingers. Whether this is truly the case is a decision I leave to you, my valued listener.
For aquasapiens pisciformis, these forelimbs adaptations are useful for enhanced maneuverability, but likely serve as poor means of propulsion. Instead, this is much better accomplished by the tail. In fact, while swimming at speed, merfolk appear to tuck their “arms” close to their sides for greater hydrodynamics, occasionally moving their hands slightly to act as a kind of rudder.
Further “streamlining” can be observed in the shoulder regions. Modified articulating surfaces of the glenohumeral joint, as well as the sternoclavicular joint in the chest, where the clavicle articulates with the sternum, also appear to result limited mobility. This restriction prevents excessive upward and forward movement of the shoulder girdle, keeping the arms in a streamlined position during swimming. But while these adaptations help to maintain a more hydrodynamic posture, they also keep merfolk from being able to effectively extend their arms overhead.
We have discussed, at some length, how the body of the so-called mermaid has adapted to its aquatic lifestyle. But beyond these more obvious changes, my research has revealed, much, much more.
Though it seems like a lifetime ago now, I can still recall capturing the specimen that would reveal so much about a species that had avoided scientific scrutiny for millennia. Its features, at once alien and familiar, are burned into my memory, vivid and unyielding. I was not alone in my efforts, but my part, it’s tempting to say I regret what transpired with that specimen. But we cannot change the past.
Apart from its morphology, one of the first features of merfolk anatomy you will likely notice are its eyes.

Eyes

In terms of vision, terrestrial creatures face relatively few challenges. At least, when compared to aquatic creatures, whose visual organs must account for exposure to both air and water, a wide range of ambient light conditions, harsh waterborne irritants, and phenomena such as refraction.
Indeed, in comparison with their land-dwelling ancestors, study of the aquasapiens pisciformis eye has reveal an extremely high level of modification.
First, in response to varying light conditions, mermaid pupils display the ability to change not only size, as one might expect, but also shape. Their pupils are able to transition from a large, horizontal oval to two near-vertical slits, serving to optimize visual perception both in air and underwater. Notably, the mermaid iris exhibits an asymmetric constriction, resulting in two slit pupils with distinct sizes, shapes, and orientations that are slightly displaced forward towards the rostrum.
In underwater environments, where light conditions differ greatly from those in air, the ability to transform the pupils to a narrower slit shape reduces the amount of incoming light that may cause glare or overstimulation.
Additionally, the asymmetric constriction of the mermaid's iris, resulting in two slit pupils with distinct sizes, shapes, and orientations, appears to play a significant role in enhancing underwater vision. The slightly forward displacement of the slit pupils towards the rostrum allows for improved forward vision and better focus on objects in front of the mermaid, and aids in reducing diffraction and scattering of light.
Lastly, their eyes have also developed a nictitating membrane, a kind of translucent third eyelid, which serves to retain moisture and shields the eye from debris and other irritants. Their fleshy eyelids, while still functional, are more recessed when open and lack lashes entirely.
In short, merfolk can see remarkable well in a variety of conditions, including low light, and in both air and water.
One notable absense, at least when compared to primates, is that of an exernal ear structure. Indeed, in my observations, the entire pinna has been eliminated, presumably to reduce drag while swimming, but also because it would have little purpose underwater.
Instead, we see little more than a small opening, which can be closed by strong muscles when underwater, preventing water from entering the ear canal, and opening when above the surface.
Further within the ear, a combination of well-developed eustachian tubes and an advanced system of sphincters and dilating muscles within their nasal passage allow for a finely-controlled the pressure equalization process during dives, while robust ossicles and tympanic membranes allow it to withstand addtional pressure.
In addition, and though more examination would be required to confirm this, I find it likely that, much like dolphins and whales, the pisciformis jaw posseses fat-filled cavities, which may transmit sound vibrations from the water to the middle ear.
Similar to the ear, the external nose and its cartiliage has been greatly reduced, while a complex set of muscles appear to have arisen surrounding the nares, or nasal openings. These muscles, which appear to include a more derived nasalis, allow for precise control of both nasal dilation and constriction. This, of course, closes the nasal passages while underwater and opens at the surface to breathe—strikingly similar to what can be observed in seals.
In general, merfolk appear to be simultaneously skittish and curious creatures. In the past, they were likely found in abundance throughout many coastal waters. Now, due to increased competition and polution, their number has likely dwindled consderably.
As a result, sightings of aquasapiens species are extraordinarily rare, and when they do occur, they are often met with harsh scepticism.
Of course, the infrequency of these sightings can also be contributed to their behavior. Unlike their deep-sea cousins, a group that merits its own discussion, merfolk spend a majority of their time in the epipelagic, or sunlight zone, but also traverse from lower depths to the surface mutiple times throughout the day, frequently mirroring the diurnal vertical migration pattern of a major food source: copepods.

Teeth and Digestion

Though their shore-dwelling ancestors had already begun to rely on the sea for food, in the transition to a fully aquatic lifestyle, the pisciformis lineage needed to adapt even further.
Fish, squid, and other small marine life compose a portion of the merfolk’s diet-but, at least among the population I have observed, their primary food source appears to be the abundant swarms of small crustaceans called copepods.
A direct reflection of this diet is found in their dentition. This species exhibits relatively large canines and incisors, suitable for grasping larger prey, while their cheek teeth are trident-shaped, allowing them to scoop the aforementioned crustaceans into their mouth and expel only water. In short, these teeth act as a kind of sieve, and provide the merfolk with a highly flexible feeding strategy.
Unfortunately, in my limited time, I was unable to ascertain the finer details of the pisciformis digestive system, but cursory inspection revealed a highly musclarized stomach and intestines, as well as what appeared to be multi-lobed, reniculated kidneys, which is undoubtedly necessary in processing the large amount of ingested saltwater. Like pinnipeds and cetaceans, osmoregulation is likely maintained via metabolic and dietary water, while incidental ingestion and dietary salt may help maintain electrolyte homeostasis.

For now, however, we will move on to another notable aspect of merfolk appearance.

Scales

At some point in the first century, famed Roman naturalist Pliny the Elder penned Naturalis Historia, one of the earliest encyclopedias. In it, he wrote of a creature called a nereid, a term often used to describe as what we might think of mermaids today.

“Nor yet is the figure generally attributed to the nereids at all a fiction; only in them, the portion of the body that resembles the human figure is still rough all over with scales. For one of these creatures was seen upon the same shores, and as it died, its plaintive murmurs were heard even by the inhabitants at a distance.”

The popular image of a mermaid with smooth, human-like skin on the upper body and fish-like scales on the lower is little more than artistic fancy.
Indeed, as Pliny noted, aquasapiens pisiciformis exhibits a layer of scales on its entire body. But in fact, these scales are unlike those found in fish or reptiles, which are usually composed of lamellar collagen bone and coated in enamel. In merfolk, these structures are largely composed of keratin, and formed by epidermal keratinocytes, which deposit filaments, which in turn, gradually harden into a relatively thin scale.

These scales, composed of the same basic elements as hair and nails in mammals, are larger and more dense along the tail, back, and neck, while thinner and more compact on the face, stomach, and nearly absent on the hands and forearms.
The purpose of these scales is likely threefold: improved hydrodynamics, camoflauge, and even resistance to biofouling, or the accumulation of microorganisms, algae, and other organisms on the skin. And though further nd more long-term observation would be necessary to be certain, varying stages of growth in the specimen I examined indicate a cycle of shedding, wherein new scales form in the deeper layers of the epidermis and gradually push older scales outward, replacing damaged or worn-out scales over time.
However, these scales likely offer very little in the way of protection, except perhaps from minor lacerations or abrasions.
Now, my valued listener, I must thank you for listening this far. Like so many records I have made, these findings likely seem to border on lunacy. But I assure you, each of these subjects is firmly grounded in reality. Even still, through the centuries, perception of the mermaid became skewed, and it moved from certainty to fantasy.
But along the way, whether in art or description, one aspect never seemed to change: that of long, flowing hair.

Hair

Indeed, though hair is absent from the entire body, like humans, aquaformis pisciformis has retained it on the head.
Initially, I was puzzled by this, as it seems this would only reduce hydrodynamics in a creature otherwise built precisely for it. After some consideration, however, I believe that it serves one major purpose: sexual selection.
In a striking example of sexual dimorphism, the kind of long hair we associate with merfolk is only present in females. In males, the hair of the head is also present, but grows shorter, and follicles are less abundant.
The exact characteristics of this long hair can vary among different mermaid species, but broadly speaking, it is useful in attracting potential mates and, for those mates, likely contributes to their overall physical attractiveness. Indeed, the volume and length of this hair may be indicators of health, genetic fitness, and reproductive potential in the context of mate selection.
It may also provide secondary advantages, such as obfuscation, breaking up their silhouette from potentional predators.
However, long hair has long been known as a desirbable trait in human females–so much so that many early bestiaries listed the mermaid’s hair as a symbol of temptation and vanity.
It is entirely possible that for pisciformis, the hair of the head is used secondarily as a kind of lure for an occasional, but very particular, source of food: humans.

Intelligence

It is difficult to say for certain what level of intelligence aquasapiens pisciformis posesses. In my severely limited interactions with these creatures, I can say they they exhibit tool use, such as rocks and bits of coral for killing prey.
And… on a personal note, after looking into the eyes of this creature, I couldn’t help but sense the workings of an intelligence that, after so many eons growing in an environment wholly different from my own, is at once vast and, potentially, unknowable.
It was precisely this experience that caused a certain… colleague… and I to so strongly disagree on what should be done with this creature… but ultimately, that descision was taken out of my hands. Unfortunately, this is the nature of the work. At least, on those long nights when sleep doesn’t come, that is what I tell myself.
In any case, it stands to reason that, having no need to develop fire, the wheel, or agriculture, pisciformis never required the kind of intelligence bestowed upon their land-dwelling cousins.
I see no evidence of a language, but cursory examination of the throat does reveal developed vocal cords, and given the fact that they appear to move in groups, it is well within the realm of possibility.
One aspect of their intelligence that is without question, however, is a notable sense of curiosity. For a time in human history, interactions with merfolk were limited to distant sightings along the same shores that birthed both species.
But as humanity entered the age of discovery and industry, sightings became more common. From the vantage point of a large ship, glimpses of a human-like form bobbing up from the waves occured more frequently–though these accounts were rarely believed.
Occasionally, humans would breach the natural boundary between land and water, whether falling from one of these ships, or perhaps swimming too far from the shore, or even drawn to what they thought was a woman out at sea.
Merfolk, naturally curious, would circle these unfortunate drifters, eventually poking and prodding, gauging the reaction of their new toy. After some time, exploratory bites became motivated by hunger. After the crossing of that line, there was no turning back.

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It is my belief that merfolk did not evolve to prey on humans, but instead, that after a less-than-friendly initial contact, a specific, rogue population developed a taste for larger mammalian prey–and one that flounders in a watery environment is far easier to subdue than one that could outswim them. And for a species that looks vaguely human at a distance, this population likely found that luring humans was not at all difficult.
However, this behavior is the exception to the rule, and a majority of merfolk are naturally shy and defensive. But whether friendly or hostile, if you were to catch a glimpse of these elusive creatures, I must warn you of a distinct problem that arises:
You can never know which one it is.

Watch the video here:

Scientific Name

Aquasapiens pisciformis