Boreolenta hydraherbensis
While Boreolenta psycrasapila survived in Zone A, don't think that it necessarily thrived. It required water in the soil to survive, which really wasn't common at all- the frigid temperatures prevented evaporation, and thus precipitation, to happen much and thus it was pretty much a frozen desert. So B. psycrasapila really only survived with the bare minimum. So it's no wonder that when a few individuals exited Zone A into Zone B, the population skyrocketed, which slowly mutated into the species of Boreolenta hydraherbensis.
The 6μm Boreolenta hydraherbensis swims in the water pockets with its reduced amount of flagella (to preserve energy for needing to swim less) finding its new host: * Lorensia clearensis*. It does a similar act to B. psycrasapila, sticking to the plant while rupturing cells and taking the nutrients from them. However, unlike its ancestor's environment, Zone B is naturally warm and its host doesn't change the temperature that much. So Boreolenta hydraherbensis attempts to keep its host alive as long as possible by slowing and weakening its toxins, requiring it to have a slower metabolism. This allows it to not completely wreck the grasslands and allow L. clearensis to survive.
The much friendly environmental factors has allowed it to completely forego a cyst form, although if absolutely necessary it still is technically encoded in its genes.