Twilight Cryosagania
As cryosaganians always thrived in cold temperatures, they found the twilight zone pleasantly hospitable, allowing twilight cryosagania to spread out from the north polar regions as long as they stayed within the cold depths. They couldn't descend too far, however, lest they lose their source of light for photosynthesis. With lower available energy levels, they no longer form colonies, living only as independent single cells, which separate after division. Additionally, they have a slightly thickened cell wall due to the greater pressure.
Otherwise, the cells are much like before. They have a pair of flagella, one on either end of the cell, which they use to swim around, but they can also use them to scoot around on the seafloor. They are sensitive to both light and temperature, instinctively maintaining a balance where they avoid too-bright light but also stay away from complete darkness. They also avoid heat sources, such as the volcanic activity of Rhino Ridge, which crosses their range.