My planet is a frozen world. Roughly the size of earth and in a perpetual ice age. The planet has very cold temperatures at night and during the day its surface becomes very bright. The intense solar radiation means that every night its beautiful landscape is illuminated by auroras.
There is some geothermal activity, mostly geysers and hot springs where some wildlife finds refuge. The planet has a single ocean with its surface entirely covered by moss with colossal root pillars descending to gather minerals. The green sea houses two ecosystems one on top and one underneath.
The snowy surface of this planet has some species of plant. The most common being the "shy moss" that turns white like the snow around it whenever it is disturbed. The other largest plant is the "bunker bud" a house sized plant that opens during the day and closes into an armored bud at nightfall. Its seeds are like hot air balloons that float far away and then fall into a new location. The only creature powerful enough to eat it is the "branchiosaurus". Named due to its branch-like spikes with retractable leaves, this peaceful giant has jaws powerful enough to pierce the plants armor.
Because of the planets conditions the creatures on the planet (including a sapient race) have some sort of photosynthesis that makes their bodies dark in color. They are nocturnal creatures that collect sunlight during the day and become active at night. This allows them to survive for a very long time without food.
I've got all of this well figured out, the ecosystem the environment even the culture of its inhabitants. The problem I'm having is with different ways to resist cold temperatures. I figured that fur inside of a folded photosynthetic membrane, insulating fat and warm blood for my creatures might be enough. But I also thought if increasing their salinity could lower the freezing point of water and give them some extra resistance. What do you guys think? Is there anything I could add? A name for the planet would also be nice.