Astrobiology, and Realistic Alien Design

Life on another planet may be very different from life familiar to us on Earth, but no matter where it lives, it must have the adaptations needed to survive in the environment it lives in. Consider the scientist in the picture here, looking into a hole in the ice at the arctic north. There is life underwater, in the cold and the dark, hanging upside down attached to frozen ice, which is quite alien and unfamiliar to most of us, and yet native to the Earth.