Mimicries
Quiet invaders
Contrary to popular belief, mimicries are not shapeshifters. They can not change form at will and spontaneously mutate. Rather, they are very small parasitic eels that take possession of another's body. Barely visible to the naked eye, they can penetrate even the tightest hole like the mouth, the anus or gills. Once inside, they carve their way to the brain using their sharp teeth to rip open internal cavities. The process, while it can heavily damage the body, is often painless for the victim, or barely noticeable.
Once it has reached the brain, the mimicry attaches itself using the two retractable hooks on both sides of its jaws and the one on the end of its tail. It usually spirals around the frontal lobe by default, however the attachment behavior may vary from species to species, as anchoring on the seat of memory requires more effort to take control of the rest of the body.
Then, they take over the mind of their host, in a similar fashion to Spheriers. In that regard, the whole species can be considered as possessing a higher mind, especially since they can dominate even great minds. But where Spheriers have to work together and can only touch the mind of a Sphere, mimicry's hooks allow them for a finer manipulation. Once the initial connection is made, it is broken only by the death of the host or its guest.
To enhance its control, a mimicry may detach from its initial anchor point and travel to another region of the brain, in order to alter the neuronal connections or utterly destroy resisting sets of neurons. If the host is fighting for control, it can become quite messy as the mimicry cuts more and more connections until the brain is nothing but a malleable mass with very reduced abilities. There have even been reports of a mimicry drowning in the blood of the host's brain after rupturing an artery during a fierce resistance.
Once the initial stage of the invasion has been completed, which means when the parasite has seized all control, then the host can effectively be considered dead. While some retain their consciousness to a certain degree, they cannot be saved. Removing the parasite would require splitting the host's head open, and we lack the technology to perform such an operation without killing the patient. In addition, the host's personality is often destroyed in the process, leaving only a living husk obeying each and every one of the parasite's orders. Thus, I advise that when a mimicry is discovered, the body is to be disposed of immediately. No rescue is possible for its victim, the merciful thing to do is to end their suffering and the evil inside them.
Practical case: Octopus invasion
Octopuses, due to their large nervous system and semi-autonomous limbs, are not the targets of choice for mimicries. However, cycles of collective effort, research and many sacrifices allowed them to find an optimal way of control. The head anchors on the sub-esophageal mass, the lower motor centers executing movement of funnel, arms, and mantle activities, while the tail whirls around to the supra-esophageal mass, the higher motor centers coordinating sensory inputs and behavioral responses.
It is unusual for the head to prefer a center of action instead of a sensory input center, but the partial autonomy of an octopus' tentacles requires finer control than most other species. It is an odd feeling, to take over such a creature, as only a tenth of its body actually feels taken over, while the others are independent of the invaded central nervous system and merely follow the orders received. For this uncanniness and the difficulty of the feat, octopods had been widely ignored by mimicries, which played a role in their downfall.
Feeding Habits
The hooks of a mimicry serve two purposes: the first one is to anchor its body to the brain and manipulate finely the neurons, and the other is to feed. They can only consume nutrients extracted from their host's blood flow. This does not take a toll on the host's body, as the mimicry is orders of magnitude smaller than the host. They can redirect a part of the blood flow to the specific area of the brain they are in, though few actually try that. Even brain-dwelling creatures fail to understand completely the working of a body and even a small modification in the vascular network can have unintended and dramatic consequences.
Due to their peculiar diet, mimicries cannot survive long without a host. They need a near-constant apport of blood because of their very fast metabolism, a heavy restriction on their free movement. It is barely enough to change host or mate. They are also weak to the biological death of their host: should the blood flow run dry, they would die with it in no time.
They feed solely on blood, and in quantities small enough to not be bothersome. We could live in relative harmony if they were satisfied with this. They can anchor on a blood vessel anywhere in the body and have a constant flow of food delivered directly to their mouth. In reality, juveniles live like this until they are mature enough to leave the parent's host and find a body to contaminate on their own. The very fact that they chose to invade our brains and rip us off our thought is a conscious and cruel choice. They are at heart a selfish species that do not know care or compassion, nor the benefice of the whole group over that of the individual. They are a plague to all our societies and should be treated as such.
Reproduction
As with all species, mimicries need to mate. They can technically reproduce using their host's body, but then their offspring would be biologically that of the host and not theirs. This process only occurs sheltered from prying eyes. First, the "male" detach himself from the host and join the "female" in hers. There are no strict genders in their species, as they are hermaphrodites. Rather, the one receiving the other in its host is considered female and the other male. The male attaches himself to the female's host's brain close to her, and they proceed to breed.
The female lays the inseminated eggs in a blood vessel and the flow will carry them while providing sufficient warmth and nutrients. When they hatch, the juvenile mimicries will fixate inside the blood membrane and feed on the endless stream of food. They will grow until they rupture the blood vessel that hatched them and join their parent in the brain. There, they are accompanied and taught the basic of life for a short time, before the parent brings her host to a place where the offspring can leave and take a body on their own.
The learning stage is short, since mimicries average eight offspring per fecundation, and many put a heavy strain on the host. Among the eight, four are likely to suffocate before finding a host or die while competing with their brethren for the control of a single host. Two are unable to overcome their victims or lose their way inside the body, and the last two succeed. This, combined with the rare periods of fertility, led the mimicry population to never become excessive.
A question that eluded most scholars for a long time was how mimicries were seemingly able to distinguish their own kin, even when they were perfectly imitating the behavior of the infected host. This secret was the key to their longevity, as it is impossible to wage war against an enemy that we cannot even detect. It is with great pride that I say my work was the one to shed light on this mystery, and I am thankful that my research was taken into consideration.
Peer recognition
The greatest strength of the mimicries was their ability to perfectly hide amongst the kin of their host. With access to their memory and habits, it was child's play to flawlessly reproduce the behavior of the host, fooling even their own families. Nonetheless, they never had a shed of doubt whether the individual before them was a regular person or one of their own kind. Thus, despite the numerous policies aiming to keep them in check and avoid the infection of the population, they are under the eyes of the ones tasked with hunting them down.
The secret lay in signatures. While the signature is unique between each individual, members of the same species and families share common traits, be they rhythm, peculiar waves or the overall shape of the sound. Mimicries imitated this signature too, but added a bit of their own, slightly mixed with that of their host. The alteration was barely noticeable unless paying close attention. Other mimicries, naturally, paid attention to such things, but not regular people who did not expect such a thing.
The work of Reef scholar Lmallni, published shortly before her death, exposed this grave secret to the whole Expanse, igniting the spark of a war that was stalled for too long.
When studied with attention, it becomes possible to distinguish the signatures of sibling parasites. It is way subtler than regular signatures but still identifiable. This was put in evidence by seeing how, when enough siblings reach adulthood, they tend to band together and create small communities. For obvious reasons, it is easier to hide in plain sight while posing as a lineage than to mix with regular individuals. Such groups can merge temporarily or permanently, depending on the situation. During the mating seasons, parasite communities may become quite large, with worrisome gatherings for a short time before each goes their way. This avoids inbreeding and allows them to form a bond with their own kin. Surveilling these unusual meetings of people with seemingly no ties may bring us closer to catching all of them in one net.
The Purge
The world had not known such a great scale conflict since the Age of Wars. Suddenly, almost every Sphere turned on the two Spheres suspected to be mimicry's homes, which were quickly destroyed. Then, the rest of the population was subjected to a signature test, with devices and expert listeners able to pick up the signature modulation. Mimicries, unable to turn off their own signature, were driven out and exterminated.
During of this period of close to an Obloggian cycle, mimicries were not the sole victims. The technology had to undergo a bit of refinement and many were falsely accused. False denunciations and popular justice over a mere suspicion were commonplace. A few Spheres fell into a state of paranoid anarchy for a time before the situation calmed down. Over a million died, of which half were real mimicries. The species was decimated, and the heads of most Spheres thought that there could not remain enough of them to perpetuate the species, and that they were doomed to wither out. Thus, instead of ensuring the end of the threat, they tried to avoid an inconsiderate amount of mistakes and innocent casualties by declaring the war won.
In current cycles, they are considered completely extinct. Multiple cycles have passed since the Purge, more than the life expectancy of three generations of mimicries. The few families that managed to hide away slowly died in exile, hidden where they could not hurt anybody.
The Obloggian Perspective
It seems like mimicries were a thing back then. Scary things, able to possess you and swim in your scales. But that's a story of the past. Even though they are probably long gone, we still have detectors that are supposed to keep them out. At this pace, they will be all but forgotten in a few cycles. It wouldn't be the first time, you know. Numerous species have emerged and disappeared over time, so many I can't even count them. Anyway, the past is not something to dwell on, especially if it is not going to be reminded.
"One thing worries me however. We now have in our hands a fatal weakness of theirs, as long as they are unable to fix it. Should a sufficient amount of those parasites be able to dissimulate their peculiar signature at will, they could continue to hide among us inconspicuously. It might be a baseless worry, but one that is worthy of addressing. In the second speech bubble joined with this message I've joined possible countermeasures that you may find equally interesting." The scholar closed the speech bubble and contemplate it for a bit. Was that enough? Had she really thought of all the possible outcomes? She was almost sure of it, but something kept eluding her. No, she had put almost a cycle's worth of study in this single speech bubble, and she was the most knowledgeable person about the mimicries. The value of this single object was now more than her own life, as no copies existed. She extended a tentacle to caress it. It seemed so fragile, so much knowledge in such a weak thing. Should it shatters, all the information she accumulated in her life would vanish into the thin water. Was it an involuntary flex? A rogue current or an abnormal stimulus? It was an accident, for sure. Nothing but an accident. She could not believe it. The remains of the shattered bubble stuck to her tentacles as she watched in horror the work of a lifetime dissolve. She heard for the last time the endless notes she took, her observation, her conclusions. Upon hearing a theory that she coined long ago and had forgotten since, she has a panicked glimpse at a mirror. She had made a mistake. She thought she was prepared, having her own signature studied each time she went out. "But that was not enough. How does it feel, to be right until the very end?" asked the voice inside her head.
Well, that's proper scary, that is. I hate them. Very good article about a veritable nightmare of a being.
Yes that was the reaction I was aiming for! Mimicries are definitely something that would terrify me underwater! Thank you for your kind words :D