Caves, Part 1

Frightful and fascinating things live in the coalseam caves below Serinarcta, an enormous cave system that now hosts a hidden realm, deep down in the dark beneath the verdant hothouse world.

It scuttles through the cave, more like a spider than a vertebrate. Up and down walls, even hanging from the ceiling. This is a world without light, and for creatures small enough, gravity doesn't limit their movements. The scuttling-thing cannot be seen, nor can it be heard over the sound of flowing water at the bottom of the cavern. Yet it is there, even if we cannot see it, cannot hear it. It could surely sense us, and from its perspective, its dark surroundings are illuminated brightly, in a way alien to human perception. The abyssal batellite, a rat-sized species of flightless moonbeast that never leaves the cave system, echolocates, producing pinging calls much too high pitched for a human to ever hear. It listens for the faint echos of every chirp, and registers how each differs slightly as it returns to its ears. Its silent calls reveal the location of every perch to jump to, of every stone to turn, and of every skittering arthropod to pounce upon and engulf in its extensible toothy maw. If we shone a light upon the creature suddenly, stopping it in its tracks for just a moment as it tries to understand something it cannot comprehend, we would see it at last. It is a ghastly, lost looking thing, frail and stark white from a life so far below the ground, where the sun never shines. We would remark at how strange its face was. Its eyes nonexistent, each a dark pinpoint deeply buried under skin in oversized, empty sockets. Its ears bizarrely pulled down into a fully round disc, stretching all the way down to its chin on either side, like a satellite dish from which no noise can escape. Far too many fingers per hand, each one gripping the rock with little hooked talons. It would shriek in fright, not able to understand the brightness that bathes it, that stimulates vestigial nerves buried in the flesh of its head, organs that have not seen such a thing in millions of years and can no longer make sense of it except to know that it is wrong. And then it would flee, running to cover, back to the shadows, a comfortable home for an alien life form never meant to be seen.

If an observer turned their flashlight to look further into the cave - a shallow, damp and winding tunnel with a roof too short even to stand up in - new horrors would soon appear. The cave roof is covered in monstrous, evil-looking things: stiff dangling tentacles lined with countless spines cover the ceiling as far as can be seen. They form coils, like deadly springs, and just why they grow here is revealed quickly when another batellite takes fright from the light, and inadvertently jumps right into one of the tendrils of the looping stranglesnare, becoming hooked. A descendant of the vampire centipedeweed, this terrifying creature is a plant, a truly carnivorous one that has lost all capacity to photosynthesize and now grows as a lithophyte, adhering its roots to solid stone, where it lies in wait as a predator. The trapped animal panics, but its struggles only cause the vine to be pulled down with its weight, tightening its coils around its victim in a fatal embrace that squeezes tighter and tighter until the animal can do nothing but squeak plaintively and hang suspending and bleeding until it dies, a slow process, for the plant has no way to deliver a final, killing blow. Even tiny drops of blood that fall to the rocks below quickly attract attention in a world fully reliant on death and decay for life to persist; giant springtails, huge and primitive insects, gather from beneath the rocks to lick the drippings from the floor as the animal they fell from still struggles hopelessly in the clutches of the snare - and they, in turn, draw the attention of other batellites, which hunt them. Meanwhile, over the course of the next twelve to sixteen hours or so, the vine will contract, coiling near its base so as to lift the prey, dead or still unfortunately alive, up to near the cave roof, and there its other leaves will move to wrap around it, protecting it from scavengers. Digestive enzymes then ooze from pores throughout its tendril, which digest the animal over more than a week. The horrifying lifestyle of the stranglesnare, and its near relatives also endemic to Serinarcta's caves, is extremely unusual among plants, which normally must either photosynthesize directly in sunlight to produce the sugars they use to make energy, or must steal them as parasites from other plants which do so. Stranglesnares utilize the flesh of animals to produce energy, converting flesh and fat into glucose usable for its energy needs through digestion in a manner unlike all other plants, but very similar to fungi. And it is, originally, from a once symbiotic fungus that these plants acquired the genes that enable this to occur.

An abyssal batellite (Discuvertus praeteritus), meaning lost disc-head, and its predator the looping stranglesnare (Falxadendron proculsolus), meaning hook-leaf far-from-the-sun.

Descended from epiphytic centipedeweeds, they evolved from species that adapted to grow in darker places within the sheltered spires of the cementrees, where they could catch small burds and molodonts that moved through the same hollow spaces looking for places to nest or hide from other enemies. With little to no light available on the inside of the cementree's protective spire, they tapped into the tree itself via mycorrhizal fungi also living there, and through their network of hyphae growing throughout the forest, linking its trees, they stole the sugars necessary for their metabolism, while continuing to utilize the carcasses of trapped animals as a source of nitrogen for growth. Some time in the last five million years their ancestors moved even further down, into the hollow cavities beneath the trees, and then made a jump from living within the cementrees to growing wholly independent of them after acquiring genes from their fungal symbiotes via horizontal gene transfer, a form of direct movement of genetic material from one organism to another, which can rarely occur between closely-associating organisms, even between different kingdoms of life. The stranglesnare has acquired the genes that allow for active digestion of dead and decaying life into energy as fungi do, freeing it not only from dependence on sunlight, but also upon other plant hosts. Not quite a "planimal" but resembling one, the stranglesnare is a "plungus" - a genetic fusion of plant and fungal kingdoms, albeit the vast majority of its genetic makeup is plant, and only a few tiny but important elements originate from outside sources. Beneficial horizontal gene transfer is rare, but it is not entirely unknown on Serina before this. It is also responsible for the cellulose-digesting abilities of thorngrazers, which acquired the necessary stomach enzyme from bacteria. Most easily occurring in situations where disparate organisms are living in very close quarters, particularly in damp places (including inside organism's bodies), these cramped, wet, and still so mysterious underground cave systems may yet hold even more examples of this strangest form of gene inheritance, a complicating factor in evolution that is only rarely able to be observed elsewhere.

But this is only one among many cave-dwelling stranglesnares, and not even the most fearsome - the most worrying of all can pounce upon their prey, more like animal than plant.

The cave chandelier is a species of stranglesnare adapted to grow in exceedingly deep and narrow caverns where large prey is only a rare visitor, often in tunnels that animals don't dwell in, but may use to transit from one larger cave to another. Here, every source of food must be taken advantage of, for there is no guarantee another will come around for a long time. This has produced a highly aggressive centipedeweed, one which is capable of actively attacking its targets at a distance.

Cave chandeliers are unusual among their genus for their lack of roots as adults. Though seedlings have them, they lose them over time, and mature plants hold themselves onto the cave roof with their oldest leaves that become strap-like with especially recurved hooks. This is because the chandelier is not sessile, limited to one spot like most plants. It can walk, and it can jump.

The tendrils of this species are lined every so often with a specialized, hypertrophied spine that resembles a hair, and can grow to a length of three feet or more. These have become feelers, and like a cat's whiskers, they let the plant gain an understanding of its surroundings. They serve to detect prey nearby in several ways, first by sensing carbon dioxide produced in animal breath, then by sensing its body heat. The hairs are lined with phytocromes, light-sensitive proteins that are common to plants and normally aid in germination by detecting ambient lighting and temperature conditions. In the chandelier, these proteins are specialized and sensitive to the infrared light spectrum given off by warm-blooded animals. Lastly, each feeler is receptive to touch. All three senses come together to comprehend stimuli - it requires at least two together in order to attack, reducing the chance of a false positive where it thinks there is food nearby but it is only a breeze.

When the plant senses breathing, "sees" body heat, or has multiple hairs touched in a span of a few seconds, it drops, reflexively releasing the hooks on its leaves that hold it to the cave and falling on top of its target, which is instantly engulfed in its deadly embrace of spiny tendrils and slowly constricted. The plant can kill anything from the size of a rat up to things approaching human size, holding them helpless and tightening its grip until they die, then digesting them over days and weeks. When it has finished feeding, the plant is able to return to its upside-down perch within a month, crawling itself over the floor and back up a wall with repeating contractions and extensions of its tendrils in a general direction, which over time heave its entire body back into position to hunt again.

Though it feeds infrequently, it uses so little energy to survive, and can gain so much nutrition from a single kill so as to survive for a year or more between meals, like a python. Cave chandeliers, which are hermaphrodites, typically flower immediately after settling back into place after a meal; their blossoms attract small cave insects, but can also self-pollinate. Seeds are later dropped and eventually are carried to new caves by flowing groundwater. Seedlings germinate low on cave walls wherever water has deposited them and feed on insects early in life. When they become strong enough, they lose their roots and begin ascending the walls to higher roosting places, and there take there place as apex cave predators.

But they are not the only dangerous creatures a visitor to this gloomy underworld may discover.

~~~

Cavecreepers are sinister-looking animals which lurk at the inlets of many of Serinarcta's northernmost caves, often displacing imps (discussed here) in regions with longer seasonal nights as one of the first animals to converge around fallen animals from the world outside and feed on these unfortunate victims. They are adapted to a world of darkness, lacking eyes as we recognize them, their skin pale and mostly hairless. They spend many hours clinging motionless to the steepest ledges of the higher caverns, out of reach of the light; they are social, and spend the days sleeping in groups, tightly huddled together like a single large mass of flesh that slowly quivers with each individual's breathing. The slightest sound of something dropping down from above, however, wakes them at once, and they move apart. Long, spindly limbs reach down the rocks, and the bravest one or two of the group begin to climb down the cave with a splayed, sideways motion, resembling a very large spider. Three sharp claws per hand and four per foot grip the rock with each step, providing sure footing. As it comes closer, following the source of the sound, an unsettling high-pitched pinging sound echos through the cave, barely audible to human ears.

The creature is echolocating, forming a map of its environment by the sound waves that return to its ears after bouncing off the cave walls and other surroundings. They can tell just by sound the shape of whatever has fallen into the cave. But that is only one clue, and if the echo does not suggest the object is moving, it can neither confirm nor deny that whatever it is might be edible. So the creature comes closer still, to a range of around 10 feet. Now, a new sense takes over. This strange organism has no visible eyes, only dark pits in its skull where they once would have been. But these eye sockets are not blind. The cavecreeper has evolved infrared-sensitive tissue within these sockets, functionally providing it with heat-sensing eyesight at close distances. In this case, it can now determine clearly that what has dropped down to the cave floor is not of their interest; it is merely a piece of moss-covered stone, no warmer than the surrounding cave. Cavecreepers ensure their heat vision is always accurate by constantly blowing back cool air from a single large nostril just ahead of their eyes, keeping the membrane colder than the surrounding air, and so avoiding false-positives. With no meal to be had yet, the cavecreeper turns back the way it came, ascending the walls once more, and returns to its fellows gathered together in their high roost.

These sinister-looking animals are birds; specifically, they are taptracker skewers, the next closest relatives of rasps, which have evolved in isolation in Serinarcta's cave systems for more than 8 million years. In many ways, they closely resemble those relatives, for they too are flightless and have especially large, hooked bills with mobile, serrated tongues that function as lower jaws. These traits are independently specialized from a common ancestor, however, and cavecreepers differ from rasps in just as many ways. They are, in many respects, neotenic skewers. Adults lack mature plumage save for sparse bristles (some which function like whiskers on their arms) and never develop eyes. They retain all three wing claws, two of which are shed during pupation in rasps and most other skewers. They move as quadrupeds rather than bipedally, and can bear weight downward on their forearms, and they are ectothermic, like skewer larvae, an adaptation that reduces their energy requirements in the cave, where the food supply is unpredictable. Though cavecreepers undergo pupation, and have not fully reverted from their multi-staged lifespan as have skuorcs, the larval and adult stages of this species have become less distinct from the other. This is true just as much for the larva as the adult, for unlike most skewers young cavecreepers must become independent predators very early in life. Though the female's eggs are deposited in a small animal carcass, which is defended by an adult from other scavengers for several weeks, this source of food is not enough to last the larvae until it is as big as those of the true rasps.

What this means is, in order to continue growing toward their large adult size, larval rasps must go off on their own as soon as their first flesh-nursery is depleted. This means that they are, by necessity, much more mobile than other flickbill larvae, able to crawl away and begin hunting for themselves at the age of just four weeks, when they are about as large as a mouse. By this time their skin has become impermeable, or nearly so, and their lungs are fully developed. Their bones have hardened enough to let them scurry across the cave, clinging to rocks with their wing claws and seeking out live prey, mostly insects at this age, which they find by scent and by the sounds they make crawling around, which are picked up by the animal's entire body as it moves along hard surfaces low to the ground. When prey is detected, the larva lunges forward and skewers it with a downward strike of its mandible, then rasps the body apart with its tongue. Growth as a larvae continues until the animal is around 2 pounds, which may take up to two years. Then it pupates, forming itself a sheltering cocoon of dried mud high up a cave wall in which it entombs itself for up to 8 months. When it emerges, it has become lanky and thin, a miniature version of the adult weighing about 10 ounces and standing about nine inches tall.

While rasps pass through a flighted life stage before their eventual flightlessness, cavecreepers never develop feathers beyond sparse hair-like filaments over the skin. Very young cavecreepers like this are still vulnerable to predation from their own species, and so are solitary and spend most of their time in small crevices and very steep cliffs the adults cannot reach them. By the time they're half grown, however, they are safe from their fellows and begin joining their groups, where they naturally slot into the lowest ranks in a surprisingly complicated social hierarchy, in which the largest female is at the top. The youngest cavecreepers are the ones relegated to scouting duties, leaving the safety of the clan to investigate each newly fallen thing into the cave, as they are the most expendable, but also the fastest to flee potential danger. In contrast, the lead female - the queen - rarely leaves a safe, elevated roost for any reason. In a given colony she will be the only reproductive adult, mating with any male of her choosing while aggressively suppressing the reproduction of other females, which she expects to bring her carcasses in which to deposit her own eggs, and then to watch them for her, so she can continue to lay more eggs. This is a thankless job for the other females, yet it is very dangerous for one to go off on her own and try to start her own colony, so that many stay around anyway. It may prove more successful to wait in the wings, doing the queen's bidding, until you, too, have grown big enough to fight her for her place. The queen has the support of her entourage to defend her most of the time, yet is left alone when the rest of the colony descend to find food. It is then than an up and coming subordinate female may take her chance to slay the leader and so take her place.

When a cavecreeper scout confirms that food has fallen into the cave, it normally alerts the rest of the colony with a series of excited pinging calls, though may play dumb and remain silent if the food available is only enough for one animal. Normally however, a large carcass or injured animal requires the teamwork of the whole colony to subdue, and as many as twenty adults can converge upon it, slashing and rending with their wicked jaws, their tongues even more mobile and jaw-like than in rasps. The sharp "teeth" on the tongue of cavecreepers are retractable, slotting away into grooves when the tongue is pulled into the throat and then shooting out when it is extended. There is a strict order of which animals get the choicest parts of the carcass, with the youngest getting the worst pickings. Males fill their crops with food not just for themselves but to regurgitate for the waiting queen back at the roost, while other females don't share with anyone.

Though adapted to live underground, cavecreepers are not well-suited to disperse through caves not close to sources of surface food. Without a flying juvenile life stage, the adults must instead travel over the ground and leave their caves when the time comes that a cave is becoming too crowded and a colony is forced to split. These travelers begin their dangerous forays in winter, when the nights are longest, and they may spend several days above ground until they find another suitable cave entrance. Males will be welcomed by most any colony, as a source of new genetics to mate with their queen. Females have it harder - they must find a vacant cave, and begin their own colony, for if they go down a hole already inhabited, the resident queen and her colony will kill them. Cavecreepers are effective at navigating in darkness, but are blind and vulnerable by day, which is likely the limiting factor to their spread further south across Serinarcta. Requiring long winter nights to migrate successfully, these animals are only found at high latitudes.

Not all cave predators leave the caves like the cavecreeper must to disperse. The wickitt is a small sawjaw endemic to several cave systems in central Serinarcta, a home it never, ever leaves. A close relative of the nightforest's twilynx, the wickitt is unmistakable for any other animal, for its specialized habitat has changed it in several strange ways from other species in this genus. The most obvious is color - the wickitt is a vibrant, scarlet red color that is most unusual among tribbetheres, especially on its face and large, satellite dish-like ears. This hue is produced from its skin, rather than its hair; its fur coat is very short, sleek and iridescent with a velvet-like texture, and jet black with a shimmering effect in the light. The wickitt is red, however, because it is not usually seen in the light at all. Wickitts have thin, heavily vascularized skin, which results in their rosy hue as blood underneath is visible without thick hair to conceal it. Red is the first color to vanish as light levels fall, and so the wickitt is rendered invisible when far below ground, its preferred place to hunt. It climbs steep, slippery cliffs with ease with its long fingers and sharp claws, and is the least bipedal sawjaw, very rarely standing on just two legs and using its tail as a very necessary third limb to aid in climbing.

Wickitts feed on a wide variety of prey; near the surface, they capture molodonts, burdles, and even prey closer to their own size like imps, ambushing them, killing with an instant bite to the throat, and dragging them away quickly in the darkness. Yet wickitts favor deeper environments than this - places where the light may never shine at all. Their primary prey of choice are burrowers, especially smols and bumblets, animals which occur in the caves at high density, but which favor low-lying, wet caverns. Following their quarry down into the depths, the wickitt squeezes itself into remarkably narrow gaps by collapsing its own ribs and compressing its skeleton; it slips through holes no wider than its own head one long arm at a time, demonstrating incredible flexibility as it slinks through underground channels just inches wide in order to reach otherwise hidden rooms and caverns where their prey hide from other enemies. Many caverns are otherwise accessible only from the water, and it is here that both the bumblets and smols find their food, using dry air pockets to raise their young - the favorite treat of the wickitt. There is just one issue with this, a problem the wickitt has developed a solution to in an unusual way. Burrowing animals come pre-adapted for a high tolerance for low-oxygen environments, for this is the norm in tunnels in the earth. Isolated caverns, with few entrances, are often very low in oxygen, and the wickitt's prey use this as an additional defense. The wickitt is a more recent colonist of the underground landscape, and has not had millions of years to adapt to endure these harsh conditions indefinitely. Its bright red color is its temporary work-around; it comes from a dense profusion of blood vessels in its extremities, which are able to absorb small amounts of oxygen from the air to maintain these tissues oxygen needs, bypassing the lungs and increasing their total ability to uptake oxygen into the body as a result; this is a very unusual ability among land animals, and allows the wickitt to endure oxygen levels of just 8% for as long as 30 minutes - a tiny fraction of the surface level oxygen, exceeding 30% in this era. The very short, sleek fur of the wickitt is this way so as to maximize exposed skin to the air. After this time, however, the animal must return to more breathable chambers; its spatial memory is unmatched, as would be assumed, for it must keep track of everywhere it goes, and remember the way back before its tolerance for the harshest reaches of its environment wears out.

Cave life has changed the wickitt in one other way, too. Because caves are consistent, and nearly always the same temperatures and environmental conditions, they have simply no need to maintain a warm body temperature. The wickett is an ectotherm, its temperature always around 79 degrees - the temperature of most caves. This reduces its caloric needs significantly, but more importantly, it means it can get by with less oxygen, allowing it to endure such long periods with such little air to breathe. Without its body having to maintain a heater at all times, energy which would go this task can be diverted to other processes. Because the caves never truly get cold, one could scarcely tell that the wickett is a cold-blooded creature, as it can remain quite active at all times, never having to worry about a sudden change of weather that could cool or overheat it.

~~~

Not everything in the coalseam caves is a carnivore, though most things will eat meat, as this is a biome without primary producers, which relies on energy falling down from above. Herbivory, at least some of the time, can nonetheless exist as long as an animal has the means to leave the caves and feed in the outside world, which some endemic species are known to do under the cover of night. Not all who pass between the borders of the two are lost - as some leave them to travel, others do so to feed.

The polyphemus is a troglodyte molodont descended from the cyclops, which has become specialized for life in the upper caves of central Serinarcta. Named after a legendary mythological cyclops, this animal has been adapting for a life underground for nearly five million years, an environment which has greatly changed its appearance. The polyphemus can still see, and has more forward-facing eyes than other tribbymaras, but it relies much more heavily on hearing to navigate - like many cave tribbets, its ears are greatly enlarged - and upon a powerful sense of smell to find food.

About as big as a sheep, but strangely proportioned with a very large head, the polyphemus is smaller than its ancestor species, a simple adaptation to less available food. It is a mostly solitary generalist which will eat anything it finds, using upward-pointing tusk-like cusps on either side of its lower tooth plate to acquire varied sources of food. These tusks are used to scrape up bacterial mats and fungal growths from cave walls, to pick roots and tubers where they grow through from the soil above, and to kill large animal prey which occasionally falls in from the many steep entrances into the cave. Saber-like, these teeth are used to gore victims in the gut from below, with the animal then using its very large neck muscles to lift up the animal and toss it, repeating until it is dead or almost so. Then, the polyphemus uses its strong jaws to tear open the abdomen and feeds quickly and fiercely, before anything else can come along and take its prize. Unlike many cave dwellers, this animal is not strictly tied to life underground, and polyphemus often climb out of the caves at night to feed on vegetation or other animal foods they can opportunistically acquire, retreating quickly back inside and disappearing into an impenetrable labyrinth of dark tunnels they have long since memorized if threatened.

Polyphemus have evolved an unusually large, round air sac on their sinus which they can inflate quickly in a threat display, either to another polyphemus or to a predator, and this structure is bioluminescent, so that when unveiled in the gloom of the cave or on a dark savannah, the animal appears to develop an immense, staring eyeball in the center of its face. The display is accompanied by a startlingly loud release of air from the animal's lungs, and serves to intimidate rivals into backing down, or frighten enemies long enough to let the creature run away and hide. The light produced in the polyphemus' crest comes from symbiotic Lactobacillus bacteria which colonize the sinus, feeding on mucous as a source of nutrients, and preventing colonization of the nasal cavity by pathogens. These bacteria produce luciferase, an oxidative enzyme, in order to glow. Though bacteria of this genus are ancient, and common in the bodies of many animals, the specific lineage of bacteria which has colonized the polyphemus' air sac evolved first within the sinus of crested thorngrazers, specifically loopalopes. It was acquired by this new host sometime in the last 3 million years - possibly, if not probably, through the scavenging of a loopalope carcass by an earlier species of cyclops. The skin of the polyphemus' air sac is only stretched thin enough for the light to be visible when it is fully extended - when at rest, the animal's forehead skin is loose and wrinkled, and the bacteria in the sinus are hidden, letting their host vanish into the dark.