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Sculk (Aspergillus tenebrisum)
The Deep Dark is inhabited primarily by an endemic mycelium-adjacent mass of fungal growth known colloquially as sculk ( Aspergillus tenebrisum ). Sculk is a decomposer, thriving off of death. It is known to grow with new decay, then lay dormant, as a deciduous tree would during the winter seasons. A. tenebrisum is identifiable as a network of twisted tendril structures, rather like common swamp vines, known as veins , which are dotted with hard, starch-filled nodules. It is not yet known whether these nodules are harvestable and edible, as potatoes are. The network has mild elasticity, and is quite spongy and quick to draw in moisture from its surroundings. The veins are deep teal in colour, and its bioluminescence reactions emit bright cyan light. Some organs of sculk have chitinous shells which are the colour of ancient human bone.
The growth of A. tenebrisum is initiated by organs known as catalysts, egg-like structures off which grow root-adjacent tendrils. The catalyst produces enzymes which are distributed through the sculk network to the site of decay to decompose the carcass, after which the roots absorb the nutrients and distribute them to the growing tips of sculk veins. Excess nutrients are stored in nodules throughout the veins, which slowly deplete over periods of dormancy. Other organs of sculk include sensors and shriekers . The sensors of sculk are so-called due to their unique exhibition of a sort of sononasty – they are tendril structures which react to sound (or, more specifically, vibrations) with bioluminescence and “clicking” sound responses. These mechanisms are yet unknown, but it is suspected that the tendrils are highly sensitive and thigmonastic, to where they can not only detect changes in pressure as small as those resulting from sound waves, but also move quickly enough to cause changes in cell shape in a manner which catalyses the bioluminescence reactions, and to rub chitinous segments against each other to produce such sounds. However, further research should be conducted to confirm these ideas. The shriekers of sculk are presumed to be an adaptation to its mutualistic relationship with Wardens. They exhibit similar sononasty to the sensors, but their response is the emulation of a sound of airy shrieking, giving them their name. These ‘shrieks’ are tuned to a frequency which attracts Wardens. It is believed that the shriekers are a defence mechanism, in which the sculk responds to unwanted attention (as from grazers, parasitic organisms, etc) by emitting ‘shrieks’ as a distress call to which Wardens respond.
It is believed colloquially by many that the sculk imprisons the souls of the dead, and that the sounds emitted by its shriekers are the souls’ cries of anguish. Due to limited peer-reviewed research on the exact mechanisms by which sculk organs produce their environmental responses, this theory cannot yet be proven or denied as a possibility. Sculk is also believed to have the ability to communicate across its entire spread, as known mycelium networks are believed to provide interspecies communication in large, aged forests. To that end, it is believed that the sculk can communicate directly with Wardens, rather than simply calling on their aid in times of crisis, perhaps through these imprisoned souls. Regardless, more research should be conducted, though care should be taken to ensure the scientist(s) remain in the good graces of the Wardens.
AUTHOR'S NOTE: Aspergillus tenebrisum is a fictitious name. Aspergillus is a real genus which contains hundreds of fungal species that form mycelium. Tenebrisum is derived from the Latin word for 'dark' in homage to sculk's biome being called the Deep Dark.