|Size||5.0m tall (3m legs, 2m body) 4m long, 800kg|
|Social Structure||Small Herds|
These large desert roaming creatures have eleven legs and a large laterally flattened cylindrical body with no discernible head structure.
Physiology & Ecology
Their long legs alternate synchronized movement, and move together like oars on an ancient galley, first one side and then the other. The eleventh leg in the back, acts like a rudder and swings on either side with each alternating stride. This pattern produces a gentle sway atop the 3m tall legs. Viewed from above the strider seems to produce a serpentine path and never quite moves in a straight line. The pace is not really fast but their endurance is endless. They never stop walking, slow and steady wins the race. They carry out nearly all bodily functions on their relentless walk. Each leg is a moisture probe. Spongy filaments around the base of each long segmented leg absorb tiny amounts of moisture trapped between grains of sand with each step. Their mass ensures that the pole like legs sink into the shifting sands with each step and the momentum of the swinging body brings the other set of legs up and forward. Cable like elastic connective tissue store and release energy very efficiently and these cross linked fiber bundles are responsible for the body's contours and shape. The eleventh leg is more flexible and has a more specialized probing ability if superficial sub surface moisture is proving to be elusive. Each leg is attached to pump three huge lung like structures. Vast mats of vascular tissues that exchange gases and pump air through a systemic network of tiny passages. Circulating air is essential for thermal regulation in the blazing hot temperatures of their native world. The flattened, near vertical 2m high body walls have large slightly over lapping plates of integumentary right handed, tightly bound, super coils of dense polypeptide chains, similar to reversed terrestrial keratins. The dorsal surface is slightly rounded and each leg pair corresponds to a body segment. The ventral body surface is open, thick filtration fibers hang in dense clumps from between the legs. These branched structures are richly supplied with circulating fluids and permit gas exchange. They also lead to the spongy air passages that permeate the shelled body. As the air is forced through the body, by the rhythmic pumping action of the well muscled legs and their attached triple billowing "lung" structures, the entire organisms body is an air purification filter. In this case optimized to remove nutrient microscopic air plankton from dusty winds of their desert planet home. This organism's vast bulk is necessary to permit energetically effective gathering of these relatively low concentrations of nutrient cells (think blue whale). The tiny wind tubes that fill the body are lined with villi like cells that trap microbes on their mucus layer and phagocytotically ingest the nutrients. In their native environment thick colonies of autotrophic photosynthesizers live across the surface of the sands. Their enzymes and photosentive pigments are tuned to the color of the local star and the composition of the native atmosphere and lack the familiar green of terrestrial producers. These striders can absorb these cells as the walk through their colonies and stir up clouds of them as they pass through. Their movement is needed to get the cells airborne and facilitate filtration and absorption. The eleventh leg re-releases inorganics and silicates without food value back into the soil. Their digestion, however efficient, is not perfect and native life have developed reproductive endospores which pass unharmed through the strider's system and use the huge striders to disseminate their genomic information into waste enriched soils. In a sense the striders move like a harvester/combine across microbial farms hidden from casual view. What looks dry and dusty is awash with a strange cellular life cycle.
Their predominate senses are olfactory based. As air passes through their bodies any water molecules and food particles trigger system wide messages that alter the animals' direction of travel. These air sensors are accurate to ppb, and they can unfailing be relied upon to move toward food and water if unmolested. When water and food are present they move in a spiraling search and collection pattern until all accessible resources are recovered, before setting out in the direction of the next highest concentration of desired components. Their tactile senses are dull over most of their insensitive thick integument. The exception is the feet, their feet have rings of sensors for balance, mechanoreceptors, for detecting flex, shear, tension forces which require adjusting the stride pattern and synchronized foot deployment. They have very sensitive thermoreceptors which help them regulate optimal operating temperatures and to move in the direction receiving the light necessary for their food source. The early dawn is the most critical time for them. The dew which collects as the sun rises is essential for survival. The absorption zones of their feet collect and quickly absorb water droplets as they are channeled over their bodies and gravity collected as it runs down their legs. The morning "drink" is often the only moisture they get all day. They will dig deeper with the rear most, eleventh leg, to access sub surface catch pockets of water. They have been known to probe the bodies of other organisms for leaking water.
Life Cycle & Reproduction
This organism has a single adult gender, but does experience genetic recombination and metamorphosis over the course of its lengthy life cycle. The eleventh leg also functions to deposit masses of embryonic offspring. These asexually produced, multi cellular embryos mass a few grams and have thick integument to prevent drying out. They burrow into the sand to find moisture and food. The quantity of young varies with how well fed the adult is and are released with the waste products as the strider walks. They can live in the sand, "swimming", digging and burrowing for the rest of their lives in an ecological niche similar to a soil based nematode. However if they encounter others of their species, regardless of parentage they begin to merge into a larger and more complex form. The genome is reshuffled, in a version of a sexual genetic recombination, except the number of parent genomes can vary widely. Powerful genetic editors perform enzymatically regulated error correction. Basically, all available genes are analyzed and the best traits wins. The remaining base pairs are recycled and reused. As embryos find each other and merge, the collective organism gets larger and larger. If energetics permit they grow into a sand swimming form that prowls below the surface collecting food. Eventually a tiny number of these embryo colonies, merge to form the larger strider form. The worms must first encyst for a period of time, equivalent to a local year. The cyst uses a vast network of subsurface root fibers to collect nutrients and water, to sustain the metamorphosis. The emergent form stand 1 meter tall and begin the walk that will last the rest of their lives. They reach full size after one hundred local years and are predicted to live in excess of one thousand, as long as they keep walking. They burst from below the sand on the hottest, driest day of the year, when the sands are loosest. The sun catalyzes and cures their hardening integument and with that first step, their billowing lungs begin the relentless search for airborne food. Their feet probe the sand for moisture and the growing cells of colonial photosynthetic producers. In their native ecosystem, as they walk above the sand, they are too big and fast for effective predation. Most life on their planet is smaller, so natural defenses are largely unneeded. Only decomposers and scavengers will eventually recycle their nutrients.
They are heterotrophic, herbivore consumers. They are always processing air borne microbial nutrients as a wandering filter/grazer. They are poikilothermic with an open respiratory/digestive system and a closed circulatory system. They are very efficient with their metabolic energy and generate very little heat. Forced ducted air cooling through out their bodies keep moving parts from building up heat. Sealed and well lubricated joints, on tough but simple legs ensure enduring reliability. The can't run, but they can walk forever. Moisture is carefully segregated from breathing and no moisture is allowed to escape that way. The relentless ciliary ladder ensures that the indigestible sands of their dust is sequestered toward the eleventh leg for deposition slowly with every swinging step. Their simple bodies are extremely difficult to injure. Their integumentary cuticle is non-cellular, and protein analogue derived. As a result it is light, strong and flexible. They slowly regenerate from nearly any injury as long as they can still move. They can replace broken legs on the march and if knocked down are extremely effective at righting themselves and regaining their feet. The legs are jointed in such a way that the entire body can be brought to rest on the surface of the sand. This is extremely rare behavior and usually indicates something is very wrong.
History & Background (Dossier)
Early colonists noticed this species immediately. Early satellite telemetry detected their surface movement and the large spirals of disturbed sands were temporarily visible from orbit, with good resolution optics, before the winds reclaimed them. They are large and move endlessly across what looked like barren sands. So obviously, they had to be put to use. Unfortunately, without much of a nervous system and no real brain to speak of, training was out of the question. Preliminary impressions were that this organism never stopped walking, didn't eat, drink, defecate or reproduce. It seemed like a violation of the laws of conservation of matter and energy. Riders needed special harnesses to keep cargo packs on their swaying bodies, as the endless motion had a habit of shaking packs loose over time. Self tightening straps were imported and tension must be maintained within a narrow range of tolerance to avoid impeding the organism. Goading and hitting the animal to indicate the direction of travel desired proved pointless. The organism was barely aware of riders or cargo. If overloaded they slow and then stop, which in their case is never good. Stationary they quickly suffocate, not walking is like holding their breath, they can do it, but not for long. During loading and unloading passengers and cargo it became necessary to build treadmills. These are used as stables as well. On the treadmill they are used to provide electrical power. With enough water and air plankton dust, they can survive walking in place for a few days. However, without the cushioning of the sand, their feet and absorption pads begin to wear out. Like a stage coach station combined with a moving sidewalk at an airport, dust strider stations are interesting places for colonists and animals alike. They walk in place while passengers and loads strap in for their gently swaying sand voyage. The relentless motion does make some humans sick. Others find it relaxing like swinging in a hammock. The only way drivers and handlers have to alter their direction of travel is with careful use of lures. The animals relentlessly move in the direction of food and water concentrations. Damp/wet materials soaked in the briny solution of local photosynthetic microbes are enough to alter the strider's course. It is hung on the end of a long fishing pole like rig just ahead of the animal and held about a meter above the sand. Subtle changes in its position and angle can cause the strider to alter course. Skilled handlers can get them to go almost anywhere. They don't back up well (almost impossible), and they really don't change speed. Think about commanding a sea sponge or coral to go where you want, and you get the idea. The striders seem to tolerate riders, as humans leak so much moisture, which their more efficient bodies and feet quickly absorb. Human respiratory gases, urine, and blood will all be quickly put to use keeping their cellular machinery working. They are useless as food, their dry, fibrous tissues are composed of biochemistry which is backward from human norms. If ingested, the nutrient value is equivalent to chewing on cellulose fibers. Several cottage industries have found uses for the extraordinary properties of the materials they are built from. Their resilience and strength are greatly prized domestically and as an export.
Travellers' Aid Society Advisory
Travellers are advised to avoid this animal if encountered in the wild, they will run over vehicles, and through camps as they are oblivious to most sensory input. If encountered with trained handlers and riders, they are mostly harmless and can be relied on for safe transport across vast distances of open desert. Passengers are guaranteed to die of thirst and starvation long before their mounts ever will. The dust they stir up can be a respiratory risk and most wear filter masks in their presence to avoid inhaling the microbes associated with them.