Among the many types of extremophiles that can live in extreme conditions, psychrophiles are microorganisms that thrive in cold environments. We actually have a lot of psychrophiles in a variety of landscapes throughout Earth, including Anthrobacter, a bacteria found in soil, and Psychrobacter, which can live in many sets of conditions and can cause human ailments.
I find psychrophiles particularly interesting because there are actually a number of large organisms on Earth that thrive under similar conditions. Other extremophiles, like anaerobes, don’t have many multi-cellular peers, but psychrophiles have something in common with the many larger cold-loving creatures on Earth.
One of my favorite large cold-loving creatures is the narwhal! Narwhals each have a giant tusk and live in Arctic waters. It’s amazing that they can thrive in such extreme conditions, as can numerous other Arctic creatures. I wonder if there could be alien narwhals in the subsurface oceans of other worlds!