Serina: Ogre Calacarna (Patreon)

With the melting of Serina's icecaps has come the return of an environment which disappeared during this period of intense glaciation: the ocean depths, so far deep that sunlight does not penetrate the countless layers of ever-deepening blue. On Earth, this is the ecosystem which takes up the most space on the Earth's crust, but Serina's seas are much shallower than Earth's, and near the end of the ice age, so much of the globe's water was locked in glaciers, virtually all of the seabed was shallow enough that it saw sunlight. With the drastic global warming at the dawn of the hothouse age, sea levels rose dramatically, flooding more of Serina than at any point in its history, and changing the topography of the globe far more drastically than any sea level rise in Earth's history. Oceans became deeper than they had ever been, and once more the seafloor in most regions became plunged into darkness, as sea levels rose over two-thousand feet in tens of millennia; a blink of an eye in both evolutionary and geological time spans. This led to the demise of one of Serina's most productive ecosystems and the grandest civilization yet seen, but the darkness has since become populated by strange, abyssal life, sustaining themselves on the marine snow that drifts from the shallows; monstrous caricatures of the animals of the surface layers.

During the hothouse age, seagoing snarks dominate the oceans of Serina, and this is no different in the bathypelagic depths, so deep that the light and warmth of starlight does not reach its murk, leaving the water pitch-black and only a few degrees above freezing. Vast shoals of mothfish, often many hundreds of billions strong, cruise through this darkness on their ceaseless migrations, following the continuous trickle of marine snow, the most immense movement of animals in all of Serina, but occurring in a realm seen by very few. These mothfish form the primary basis of a strange food web of abyssal hunters, as larger fish, jellies, predaceous snarks, and deep-diving seabirds rely predominantly on them. And these are hunted by the nightmare of the depths, an invisible hunter that dispatches prey with massive, snaggle-toothed jaws. Over five metres in length and weighing up to two tonnes, this is the ogre calacarna, the top of the food chain in a world of permanent gloom.

Huge eyeballs, larger than grapefruits, are sensitive to the tiniest emissions of light, allowing it to pick out the faint outlines of prey illuminated by its bioluminescent antennae, which are each split into two branches (giving the calacarna the appearance of having four antennae). These are extraordinarily fine-tuned sensory organs and greatly elongated for maximum effectiveness, able to pick out the minute vibrational movements of swimming creatures from hundreds of metres away and detect scents in the water column carried for miles on the current, from above, below, and either side, giving it a fully three-dimensional awareness of its surroundings despite visibility being zero. The tips emit a strong red glow, allowing it to see many red deep-sea animals; this far from sunlight, red as a colour does not normally show up and many inhabitants of the deep sea have lost the ability to detect it, so numerous denizens of this environment have evolved to be red-coloured, thereby making themselves functionally invisible. However, a few predators, such as the ogre calacarna retain the ability to see red and emit red bioluminescence, as it is both invisible to most other animals and lights up the previously invisible red animals. The ogre calacarna itself also takes on a red colour while travelling through the deep sea.

Its huge tooth-like mandibular projections are used for the dispatching of prey. Because prey is widely dispersed in the deep sea and it could be many months between meals, it is imperative that it is able to subdue anything it comes across. Its primary diet consists of large, soft-bodied invertebrates, like giant abyssal jellyfish, pelagic annelids, free-floating reef snails, and smaller snark species, with its huge serrations designed to pierce, shred, and snag their flesh. Escape is unlikely once bitten, as the calacarna attempts to inflict immediate devastating wounds to cripple the animal should it prove too powerful to subdue easily. Smaller vertebrate swimmers are also occasional targets, usually caught in vertical migrations when they travel to near-surface waters, catching their prey while asleep, using their superior nocturnal senses to their advantage against animals used to sunlit conditions. They are also a regular sight at carcasses, either on the seafloor or, less commonly, floating at the surface, as their superbly developed olfactory pores allow them to detect the faint waft of rot in the water over vast distances. A floating carcass is one of the few factors which will drag them to the surface in the daytime; to prevent from blinding themselves, the calacarnas retract most of their eyeballs into their stalks to let only a pinprick of light in. The fall of a large carcass into the depths is also one of the few times where calacarnas will encounter one another, and this is most often when they mate (as the glut of meat will satiate their hunger aggression for a while, although they just as often feed on other scavengers as well as the body itself).

The floating forest, a vast oasis in the middle of a marine desert, creates a glut of nutrients all the way to the seafloor, as the activities of all the life above drifts downwards as a continuous blizzard of marine snow and other scraps, resulting the most ecologically dense parts of the deep sea on Serina, thousands of feet below the bustle of the oceanic seaweed jungle. As a result, the ogre calacarna population occur in their greatest number and proximity beneath the floating forest, and it is the region's largest resident predator. They rise from the darkness at night to scour the floating forest, ready to snatch any animal caught out in the open or not well-hidden enough in the rafts of macroalgae, like some sort of aquatic bogeyman. Its acute senses, well-adapted for darkness, give it a superb edge over the diurnal surface dwellers at night, but the cryptic colouration of many floating forest inhabitants, and their ability to retreat into the tangled vegetation beyond their reach, makes the hunt far from easy.

This is the only region where ogre calacarnas regularly associate in close proximity with one another, as they are otherwise one of the most solitary calacarna species, encountering each other only to mate and being independent from birth. Groups of them systematically navigate the under-storey, through the groves of seaweed widely spaced enough for them to swim through, and work together to tear apart and dismember prey quickly, whereas they will otherwise fight each other aggressively for food. As large predators are uncommon so far out at sea, they have little competition for prey here. As ogre calacarnas are adapted to survive long periods without food, an individual calacarna therefore only rises to feed once every few months, not every night, which prevents them from majorly impacting the populations of floating forest denizens, and may just as often only make transient visits to the regions, travelling thousands of miles across the ocean in the meantime. For such an abyssal specialist, the surface world of the floating forest is merely a pitstop in its ceaseless journeys in the deep-sea.

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This is a sponsored commission for a species of large deep-sea calacarna which is found in the floating forest and is one of the region's largest predators (I dunno if there'll be others).