When in motion, it creates a blurred impression of a dark animal speeding over the ice. It is a rare sight to see this creature as it dashes across the glacier.
The rimerunner is, like most of Darwin IV's monopedaliens, a ricochetal saltator, equipped with one powerful leg attached to a complex pelvis. This small species, unlike its ground-dwelling cousins, is not particularly fast, a fact to do with the problems inherent in traveling over ice. Its dark, dorsal markings give it a hooded and somewhat threatening appearance.As it lifts its broad, three-toed foot it shows one adaptation that increases traction upon the ice. The padded sole of its foot is deeply channeled and grooved, and with each footfall the pad expands and grips the ice. Each fold probably possesses some additional microstructure to further enhance traction.
The most singular aspect of the rimerunner is the nearly independent "sensory packet" that proceeds the animal as it moves about. There is also a parachute-shaped structure; it looks like some unfortunate prey that is in imminent danger of being caught by the rimerunner. Indeed, the monopedalien halts only after its "face" has split vertically and the "victim" has been sucked within. The assumption that the beast has fed cannot be further from the truth - presently the animal ejects its "prey" and begins to run again.
The domed, orange structure is attached to the rimerunner by the thinnest of neural cables. There are numerous siphon holes on the flattened rear of the structure, each puffing continuously to keep it ahead of the trailing body. It is a marvel of physiological engineering and, even now, its function is not entirely certain. The rimerunner's sonar clearly emanates from its body, and it is imagined that most of its other senses do as well. Looking closely at the structure of the floating organ, there is a tiny, iris-like opening at the front of the organ, and it is reasoned that perhaps it is a primitive light-gathering structure. Whether it is evolving or degenerating, whether it is a radical advance in Darwinian senses or an antiquated vestige that is in the process of being discarded, there is no way of knowing. It must be vestigial.At times, creatures like the rimerunner can end up being the hosts of carver-wing oothecae.