The river rustcell replaced its ancestor, the pestcell. Much more successful than its ancestor, it inhabits the small streams, lakes, mud puddles, and seasonal ponds that dot the west polar scrub. An example of convergent evolution, it closely resembles its relative the yokto rustcell. If it is removed from a wet environment, or put through some other sort of stress, it will divide rapidly into many endospores, which will remain dormant until more viable conditions become available. It no longer is multicellular, preferring unicellularity to allow each cell to receive the maximum number of nutrients possible. Likewise, it has also found that simply letting the wind and water carry it far and wide is much more cost-effective than a plasmodial structure.