Biome Profile: Great Raft Reef - Empyrgloamic Region

Sunlight forms the ecosystem basis at the outermost regions of the great raft reef. From phytoplankton to triggernotle to jetleech, everything lives as they would in a minor raft reef adjacent to land. And yet, this comfortable little ring of warmth stops at some point. Both horizontally and vertically, sunlight is boxed out. From the top by meters of dead wood, from the side by fathoms of ocean. Any animal unlucky enough to get stranded here starve if they are not first get picked off by native inhabitants. Here is a habitat of rot, where the primary mode of production is saprotrophy of the very substrate everything lives under. This is the empyrgloamic region, where life thrives in a parallel ecosystem.

The empyrgloamic zone forms a ring at the centre of the great raft reef. This region acts as a natural barrier, cutting off biotic interchange between the outer photic zone and the world ocean by shadowing all light. As such, life between the two areas are drastically different, with only some shared inhabitants which can readily traverse the dark. Animals tresspassing from other parts of the great raft reef exploit irregular formations in the woodwork to their own benefit. Most often, this is by hopping between lit blowholes formed by waterlogged wood breaking from the raft and sinking to the bottom. However, there are multiple other unconventional ways to bypass the barrier. One not accessible to most aquatic animals is the apoplotan region, the part of the great raft reef which lies above sea level. The apoplotan region is in and of itself quite the enigmatic habitat, with kilometers of wood and junk spanning the horizon and nothing else in sight. Once you dig past the surface, however, the even stranger true nature of this area reveals: waterlogged tunnels dug by fossorial animals weave from the top to the depths, each supporting communities of saprotrophic animals. Semi-terrestrial creatures such as fusejaws travel through these tunnels to the surface and drag themselves across the raft's top, careful not to get picked off by flying placoderms. For this reason, the two lit zones of the great raft reef share a lot of their air-breathing inhabitants despite their seperation. Benthic animals are even less inhibited; the lack of light in the empyrgloamic benthos is no different from the darkness everywhere else.

You would expect for what has been said about the empyrgloamic region that it is a lightless void, but this could not be further from the truth. The floatsam here is knitted together by bryozoans which shimmer as if they were stars in the night sky. Dangling crinoids with 20 meter long stalks siphon the water for detritus, their seams gleaming in neon hues. Almost every organism here visible to the human eye has evolved some form of bioluminescence.

The leading hypothesis proposed by the late Wray expeditionary team was a chain reaction near the beginning of the empyrgloamic region's creation. At first, the region would be truly lightless and its fauna nearly blind. Some animals at the peripheral zones, however, might have evolved eyes hypersensitive to light. Their predators and prey, including the reefbuilders, may have exploited this through bioluminescence, blinding or disorienting them with flahses. As the outer parts of the empyrgloamic region began lighting up, it may have triggered those deeper in to evolve sensitive eyes as well, before the cycle would repeat. This would suggest that bioluminescence and functional eyes were evolved independantly across very many clades for their own reasons, be it protection, predation, or communication. Indeed, a recent genetic survey of empyrgloamic shroudeye triggernotles finds that they likely evolved luminescence at least 5 times across a span of 7 million years.

The base of the empyrgloamic food web is not sunlight, like the rest of the great raft reef, but wood. Bacteria serves as the primary 'producers', being the most prolific saprotrophs. Their films form on every surface which small fish and jetleeches graze upon. Deeper into the wood, xylophagous plants and lichen sink their roots. Though it seems this degeneration would be detrimental to the raft's structural integrity, the roots bind logs together more tightly, akin to the effect terrestrial plants have on soil.

In deficit of food, life has had to adapt to extreme ways to survive. Most empyrgloamic animals have very low metabolic rates, with most being ectotherms that can go months without a substantial meal. Large carcasses are rare prize to be faught over in immense feeding frenzies. Team Wray's former captain, Anri Patel, left this account of such a sighting.

"...A giant notle, perhaps of old age, perhaps of battle wounds, took a plunge into the abyss, never to return. A pod of raftsnakes frenzied as they smelled the scent of fresh blood, and hurried to gulp it down, as even that were a precious commodity. Before the corpse could fully sink, a giant - in a relative sense, as size is hard to reach here - rectangular animal approached. Its segments burst into flashes of cyan, blue and green as a standard threat display. Despite the show, the raftsnakes ignored it. In reponse, the animal suddenly ejected a shoal of small triggernotles from its back, which swarmed the dead notle, biting and darting at their competitors while the large creature pushed away the carcass with brute force. The animal dimmed its lights and dissapeared into the abyss as quickly as it had materialized, not to be seen again..."

The creature was in fact a large decapneumid jetleech, a 3.2 meter long verdant zestörmada (Laternatariigera illustris), one of the largest of its kind. Zestörmadas slink around silently, conserving energy. Slow bursts from the exhaust propell it along slowly, with jet propulsion alternating in patterns until needed, improving efficiency. Zestörmadas have a slow top speed regardless, perhaps a side effect of gigantism.

Eyes in all directions allow zestörmadas to scan for any threats and food items that they may come across. As they flair to life, turning on their bioluminescence, their many eyes glow in unison. Its fins and pneumatic outlets form its oddly rectangular shape, lined with lights. Two tail rudder fins extend from the back, acting a stabilizers to the rectangular body, as the creature is quite thin from a frontal view. Similarly, the end of the body is also raised up and forms a tail fin to prevent the creature being flipped over easily. At the top, fillamentous skin extensions offer tethers for its little triggernotle symbionts, the zestörmadas' most fascinating adaptation.

The notles in question, the wasserhansas, don't seem to be anything special outwardly. Their fleshy parts sport similar bioluminescent organs to their hosts, powered by bacteria which emit or withhold light depending if energy is received. A delay in energy transport makes them shine consecutively, and zestörmadas can even control their signals to communicate with wasserhansas.

Wasserhansas rely on the zestörmada for protection and reproduction while they do most the hunting and cleaning, one of their ancestral adaptations. On the back of the jetleech are fillaments that the notles cling to while they lie dormant and deposit their newborns. Wasserhansa swarms primarily deposit food to their hosts and their young, only taking the basic nutrients they need to survive.

Wasserhansas live fast and die young. Generations are short and have high rates of overturn, especially considering their casualties when hunting. It is not uncommon for the zestörmada to even directly consume an aged wasserhansa when new generations mature; it can only carry a set number of symbiotes.

During fights for food, wasserhansas defend their host to the death. This is because their next generation is suited within the jetleech, and its fall would bring the end of the colony. For this reason, older wasserhansas which have had opportunities to reproduce already will fight especially viciously, compared to the relative cowardice of newly matured wasserhansas. Even when a zestörmada dies, its fleet stays with it - at least until all their deposited young mature.

As the fossil record of the empyrgloamian region is a mystery, one can only infer the notle symbiont's origins from living relatives, such as dartfish. Dartfish are a common sight in the raft reef, clinging onto massive jetleeches like remoras. Wasserhansas might have started out similar, swimming with ur-zestörmadas for protection and travel. Eventually, they might have used their jetleech protectors as mobile nurseries, from which their current mutualism emerges.

A sinister parellel relationship, however, proved just as successful; the closest living relatives of wasserhansas are endoparasitic. These triggernotles attach to the host after a free swimming period, and eat them from the inside out. Once fully grown, they deposit their young and emerge from the skin, like an aquatic version of botflies.

Zestörmadas are largely solitary as they need to feed a whole fleet of lesser fish. Though they usually ignore others of their own species, encounters between individuals with large size differences result stunning exchanges of triggernotles swarming around both competitors. They are more tolerant when they want to mate. Interestingly, the wasserhansa also exchange and mate with their other fleet at this time, and even swap members, encouraging genetic diversity.

Though zestörmadas are generally quite large, aggressive smaller species are not uncommon. They ditch the rectangular bodyplan for sleeker one and actively pursue their prey. The smallest ones can be around only 10cm long, although at that size, it is unclear what their symbionts are fore. Interestingly, there have been no zestörmadas that have completely lost their symbiosis once they evolved it, perhaps either suggesting it is that good or the jetleech itself lack the ability to survive on its own again. Even though zestörmadas evolved and thrived in the empyrgloamic region, many have since moved out and diversified in different habitats. Forged in fire of such a harsh habitat, they are quite the dangerous sort once released to the rest of the dome.

Not all denisans of the Great Raft Reef have layers of complex mutualism and symbiosis. This western quaffophion (Pneumostoma occidentalis), a vigintipneumid jetleech, is far simpler behaviorally, but it swells to sizes far exceeding the largest zestörmadas. I suppose there are some things the test of time cannot beat.

Molecular studies imply that quaffophions have stayed much the same for millions of years, perhaps since the formation of the empyrgloamic region. Its odd mouth is located in almost in the middle of the body and raised up in a proboscis, much thinner and smaller in comparison to its grotesquely hypertrophied first pair of oral tentacles. These tentacles now stretch foward from the main body like a head. It is the functional mouth after all. The inside of these tentacles are lined with keratinous spikes, almost like the teeth of a lamprey. Circular muscles all around the tentacle allow it to clamp down with great strength, crushing anything it sucks in. The rest of the animal looks quite basal, but looks can be deceiving. The rear jets are surprisingly advanced, allowing it to move in bursts of speed. Otherwise, it pushes water out slowly in accordance to its breathing. Perhaps for hydrodynamics, the setae have been largely lost or reduced, and it possesses mild countershading to account for the raft's light.

The true heads of most quaffophions have been repurposed into a dorsal fin. Even as a fin, the head is functional as a sensory organ, and although their eyesight is quite poor, it is made up for by their other sensory abilities. In some species though, particularly non pelagic ones, their head has been fused into the body entirely, with the peering eyes similar to that of tetrapneumid jetleeches. Using these adaptations, quaffophions are successful hunters. Unlike other jetleeches, they are quite solitary not out of choice, but by nature; their brain anatomy is quite constrained, limiting their intelligence.

Quaffophions are weird in that they almost have no living relatives. Shockingly enough, recent molecular studies have revealed one of their closest relatives to be a dorsoventrally-flattened benthic scavenger. Beyond them, they might as well be equally related to all vigintipneumid jetleeches.

Quaffophions might be one of the earliest clades to enter the empyrgloamic region, being here for as long for their clade has existed. Though primitive, their anatomy has clearly withstood the test of time. Despite coming in a variety of shapes, the trait they all share is their tentacle-head, which they have morphed into a variety of purposes. Some blackwater quaffophions have modified into a wide constrictive tube to hold onto their prey as their proboscis sucks out their juices. Another species, possessing a sharper, teardrop shaped arrowhead, slices through the water to skewer their prey. A family has even evolved fin-like projections on their head tentacle, similar to hammerhead sharks on earth. The two fins stabilize the animal during intense propulsion, and the electroreceptive and light sensitive organs on it that allow it to scan for any prey lurking in the vicinity. Indeed, electroreception is a good adaptation for life in the darkness, and many different creatures share this trait too.

It is not just the upper seplotan tunnels where secondarily aquatic animals thrive. A creature, almost invisible to the naked eye without careful observation, lurks these crevices. With sophisticated camoflage and impressive patience, it is a cunning predator that fades into the cover of darkness. The creature, an aquatic geophilomorph centipede, is a wrottplank (Sanidathirio pateli), well hidden even in the above photo.

Anatomically, the wrottplank really is not that different from a normal aquatic centipede, but what sets it apart is its unusual hide. Its segments have cuticular protrusions that stick out to resemble wood, and it's fins look rought and cracked. Small epiphytic bryozoans encrust adults which no longer moult, as if to emulate the lights of the reef. Though it is nearly impossible to see a wrottplank, the fact that electroreception is a common adaptation in the reef means they still need to pick their fights carefully.

Wrottplanks likely evolved from benthic centipedes. Their flat fins originally used as traversing the seabed were repurposed as grasping limbs with hooked ends when they immigrated to the reef. Though wrottplanks can swim effortlessly upside down, they do need to rest, and so they hug onto the logs when they sleep. This clade diversified into a plethora of forms, being "reverse benthic" animals, clinging onto the roof of the raft reef. Various members of this clade have specialized into different diets, like on bryozoans or crinoids. These foraging members superficially resemble flatback millipedes, likely evolving a similar shape out of defence. Some of their relatives are wood eaters, stealing xylophagous bacteria from crustaceans they eat as juveniles.

Wrottplanks are suprisgly tolerant of members of the same species, some even coexisting near each other. When two members meet each other, they will become increasingly wary but nevertheless try to stay in proximity of each other where they can ambush large prey together in a mob fashion. However, this alliance is temporary and strained; once the hunt is over, they'll fight over the carcass. On occasions, kleptoparatism has been witnessed when a wrottplank grabs a small prey item and flees.. After mating, neither parents care for the young, and the eggs are simply deposited somewhere in the reef. The long and thin eggcases, with "branches" growing out of them, lodge themselves within the tunnels of the layer. Once born, the young wriggle out and have more free swimming lives. Mortality rates at this stage are high, and adults won't hesitate to eat them. Once the juveniles reach a large enough size, they will settle down and become reverse benthic. Not just wrottplanks, but their numerous relatives do this as well, another hint to their pasts. Despite seeming such a simple creature, it hides inumerable untold secrets.

Not just centipedes, other anguiform creatures roam the depths too. Unlike centipedes, with their borrowed luminescence, this comparatively much softer creature, a common glimmershnake (Luciophis vulgaris), slithers around with a full coating of its own light. As its spotted, it wriggles away, narrowing avoiding the maw of the aggressor. It spins and contorts, unleashing a brilliant radiance, blinding its predator. It darts away in time into a raft holes, the predator crashes into the reef in confusion and slowly slinking away. Minutes later, it shows up on the surface of the raft again, and baths in the sunlight. On the surface however, it looks incredibly mundane, with no signs of its resplendence. After a brief scuffle with a centipede, the glimmershnake descends. It starts glowing as soon as it hits the light starved tunnels, it entire body lights up as if there was a switch. How does this happen?

It has to do with a little trick called phosphorescence. Underneath the glimmershnake's skin cells are chemicals which absorb light at a short wavelength above the raft. When the glimmershnake descends into the water, these chemicals then emit light at longer wavelengths which are visible. By having different sets of these chemicals, it produces lights with different patterns. To supplement its phosphorescent chemicals, glimmershnakes needs to ingest minerals occasionally on the seabed.

Light is one of the few adaptation in the glimmershnakes' arsenals that let them be so diverse. Multiple aquatic shellsnake clades respire through their skin, and can stay in the sea for up to half and hour and more. Glimmershnakes are no exception: up to 20% of their oxygen needs are facillitated by curtaneous respiration. Ironically, the eyesight of glimmershnakes are quite poor, especially the semi aquatic ones, so they mainly rely on chemoreception to sense their way around.

A surprising number of of glimmershnakes also exhibit symbiosis with crinoids. Some small glimmershnakes, such as the jestershnakes (family Pierrophidae), bait predators into charging into venomous predatory crinoids with their bright glow. These venemous crinoids will protect their bait intently, tucking its feeding arm in on call, with the shnake following close behind. Jestershnakes protect their hosts as well, biting at any durophagous animals that dare intrude their homes. Some jestershnakes also serve as cleaners for the largest of the crinoids, almost treeline organisms with roots.

The diversity of notles in the Great Raft Reef is also not to be underestimated. For instance, this long and slender polebill (Telorostrum ingens) is amongst the fastest of its kind. This speedy predator zooms around, smashing its jaws into any prey it sees, like an aquatic version of a skewer. Large, muscled fins coupled with a streamlined body, and with finlets fashioned out of the hard body armor make it unavoidable. Its fins propell it along at high speeds which allows it to ram into objects. The jaws of a polebill are extremely tough and somewhat fused, which present a problem for swallowing. As such, they possess an extremely long tougue to pull prey items into their true mouth.

The upper eye of the polebill points straight forwards, yet so does the lower. Such symetricality is unusual for such a larger triggernotle. The reason for this is its huge jaws, which block vision. As such, polebills have large blind areas in front which they compensate with the eye placement.

Polebills evolved from fast-swimming triggernotles which utilize sustained swimming to chase down their prey. Although polejaws did not originate in the reef, they have found a lot of success within it. In particular, it is able to fool a lot of the electroreceptive animals that it preys on. The jaw itself has few nerves as it is fused and immovable, so all the electrosensory organs pick up is the main body, quite far from the snout tip. polebills use this to trick organisms into detecting the body while the jaw is already near it, impaling and devouring the animal. Polebills outside of the empyrgloamic region are pack hunting animals, but interestingly, raft reef polebills are both solo hunters and larger in size. Perhaps it is simply impossible to sustain so many active creatures working together.

Besides just polebills, a wide variety of triggernotles and metamorphic notles trive in the empyrloamic region, from giant "herbivorous" sunfish-like ones, which despite their large size feed on only notle larvae and bryozoans, using their pure size to scare off would be predators, to tiny cleaning ones that, not unlike shellsnakes, clean and maintain symbionts, be it crinoids or jetleeches. As long as sunlight never penetrates the dense flotsam, this realm of twilight will persist, denying passage to those that live under the sun, and nourishing its own unique lightless habitat.