Crysfortress Shell

In the sheltered riparian zones of the Slarti watershed, the crystank complex had eked out a living. Many tens of millions of years have passed worth of climatic shifts, most crucially that the pleasant temperate climes of the Cheatsian Period have long since passed and in its place is are brisk, brutal winters and pitiful, fleeting summers - climatic patterns that persist throughout the Slarti watershed to this day. Throughout these times, the crystank complex and a handful of other otherwise-maladapted denizens of the watershed maintained populations just genetically diverse enough to persist without succumbing to inbreeding; but as the biosphere enters the Bonian Period, a combination of competitive pressures and the climate of the biome itself have driven the aged crystank complex closer to extinction than before. Nonetheless, hope is not entirely lost for the old populations of Slarti. While much of the ancestral stock is indeed doomed, their respective lineages still have a window of carrying their evolutionary history beyond this proverbial deathtrap, either by way of exodus or developing adaptations beneficial in the watershed’s current conditions; in the case of the Crysfortress Walker and Shell, both a southward emigration and the appearance of adaptations to withstand the polar climates of north-central Drake have occurred.

General Adaptations
Outwardly, the Crysfortress Shell hadn’t changed much from its ancestry, save for a more dome-like shape, shorter marginal crystallines, and overall smaller size; instead, much of the changes between it and the Crystank Shell have taken place inside: In such high latitudes (and relative altitudes), reprieves of warmth during the summer are rather brief, and considering that winter days are dominated by frigid darkness with dim glows of sunlight interspersed, the ancestral evergreen of the Crystank Shell isn’t enough to withstand what the seasons bring. With the Crysfortress Shell however, it has become a more deciduous crystal flora, changing colors and internal functions as the seasons pass. With spring and summer, it is flush with bold green quite similar to its ancestral stock; but with the coming of autumn and the first telltale signs of winter, it takes on a yellow-gold hue and then to a bold red later into the fall, during which it stocks up on its overwinter supply of precious sugars. These pigment colors change in response to which wavelengths of light the crystal is exposed to during the days leading to winter. Once it has sufficiently stocked up on sugars (usually late into autumn), the crystal starts producing chemicals signaling its photosynthetic cells to cease all such reactions, resulting in the greater organism turning a gloomy gray-mauve - an eerie sight should one shove away the dense snow concealing it. Some of the stockpile sugars produced during the short autumn would be refined into antifreeze chemicals, further ensuring neither it or its intertwined walker host perish in the winter’s dark embrace. Only by the first thaw of spring does the crystal begin to regain its green pigment, and thereby its photosynthetic functions. Notably, populations to the far south such as those found in Drake Temperate Woodland experience longer periods of photosynthetic function and somewhat shorter winters, and consequently, produce antifreeze compounds with much less frequency. The dome-like silhouette of the Crysfortress Shell is also beneficial for when its native climes turn cold. As its shape has relatively little surface area, less heat would be dissipated out of the crystal, which does help with withstanding winter. The serrated array of crystallines rimming the crystal’s base provide both it and the walker host with defense. Should a predator of either the crystal or the walker encounter the complex (e.g. the Glowspike), the sharpness of the rim crystallines cut into soft flesh, making for an effective deterrent in any season. Nonetheless, the Crysfortress Shell does retain much of its ancestral biology: it possesses a network of many specialized rhizoids, some tapping into the Crysfortress Walker’s digestive tract where its blood can carry and distribute the sugars its crystal host has produced, while others are integrated within the walker’s circulatory network - ferrying blood into the crystal’s own networks in which the nutrients the walker obtained are taken in by the crystal’s tissues. It is also worth noting that both the Crysfortress Shell and Walker readily exchange gases amongst each other via this intertwined network, with the walker supplying its shell with extra CO2, and the shell giving the walker some oxygen in return. Other rhizoids still have intertwined with the walker’s nervous system; the crystal detects visual information via an array of photoreceptive chitinous lenses, and the walker processes and acts upon this sensory input, as it possesses very little sensory functions beyond a rudimentary chemoreceptive sense - integral for the crysfortress complex to move a more food-abundant or photosynthesis-friendly location or to escape predation; the shell can also secrete hormones to influence its walker host into certain actions and behaviors, most notably with reproductive functions.

Reproduction
Breeding behaviors typically start to occur somewhat late in the spring - right when the Crysfortress Walker’s fare options are at their most abundant and the climate is already fairly warm. At some point after a fresh molt, the Crysfortress Shell secretes hormones into the host’s portion of the nervous complex, prompting it to actively seek a mate. Upon encountering another crysfortress complex, both the shell and walker are inspected for fitness via the input of that potential partner complex’s appearance and hormones. Should that partner be deemed of sufficiently fit genetics, the inspecting complex will deposit a packet containing both the walker’s and the shell’s sperm, which she will readily accept. With spermatocytes conjugated with their respective components’ gametes, these will develop into both the walker’s eggs and the shell’s zoospores. The Crysfortress Shell’s gametophores are located on the end neighboring its host’s gonads, minimizing distance between reproductive vectors. This is significant as, unlike previous crystal-walker complexes, Crysfortress Shell spores bury themselves into host eggs, ensuring a greater form of host-symbiont integration. Zygote shell spores are of zoospore form, possessing robust flagella with which to crawl along their host’s surfaces. Keenly guided by particular chemical signatures, these zoospores make their march right into the oviduct, all within a critical period in which the eggs have not completely developed their outer shells; this is important as this is the only time when the zoospores can insert themselves into the eggs containing the host walker’s own zygotes. Once the host’s eggs have been expelled, the spores begin to develop into new crystals themselves, fueling their growth by leeching off negligible shares of energy from the embryonic walker. Although seemingly separate at this state, as both embryos develop they will become increasingly interdependent with each other, with the nascent walker developing a seam of exposed tissue along its dorsal axis - right where the shell will intertwine its own immature tissues. Both the developing walker and shell will attain the same sex. Upon hatching, both shell and walker have become a single composite unit, complete with the full integration of circulatory and nervous tissues. Aside from carrying the developing eggs with her rearmost legs, the mother walker invests no parental care otherwise, making both her and her shell r-strategists - producing numerous, usually independent offspring per breeding. The offspring crysfortress complexes will then part their own ways into a world teeming with beasts seeking to eat them, and conditions which will turn hostile in a matter of months. Of a single clutch of a hundred crysfortress complex eggs, few will survive to adulthood.

Relationships with Other Crystank Biota
With the ancestral crystank complex, the walker and the crystal aren’t the only interacting organisms; also closely associated are the epiphytic Crystank Flasprout and the sporophagous Crystank Crystalworm. For one cause or another however, both lineages are absent with the crysfortress complex, whether due to changes in the complex’s biology or merely due to population drift. The flasprout symbionts have diverged from life within the Crysfortress Shell some point before the ancestral population moved southward, thus these organisms are not present in this offshoot shell-walker complex, and the walker no longer manufactures the chemicals responsible for inducing its former symbionts to flash and reproduce en-masse. The crystalworms likewise cannot feed on the spores of the Crysfortress Shell, as they now develop within the eggs of the Crysfortress Walker; thus the complex split is left ignored by the crystalworms.