When I was younger I came up with a creature that seemed to contradict itself. It was made of some frozen material, but it had a large back fin in order to get warmth from the sun. I'm revisiting the idea, and wondering if such a creature would actually work, and what it might be made of.
If it can't be ice then what about a material that melts at a lower temperature? What's one that would melt at the temperature and pressure that we're used to and could work for life?
The planet it lives on has ammonia oceans, chlorine atmosphere, lower temperature than Earth's, and high enough atmospheric pressure that the mineral olivine can form on the surface.