Although blue is the color most often associated with the world’s oceans, black is a far more apt descriptor for nearly 90 percent of our planet’s waters. Descending beneath the surface, the seemingly endless, light-flooded blue quickly fades, leaving nothing but utter darkness by a depth of roughly 200 meters (650 feet). Here, the largely unexplored and perpetually dark deep sea begins—a hidden, dreamlike world filled with fantastically weird creatures: gliding glass squid, flitting sea butterflies, and lurking viperfish.

Last winter, photographer and marine biologist Solvin Zankl joined a scientific expedition led by the GEOMAR research center in Germany to conduct deep sea biodiversity assessments around the islands of Cape Verde. The team explored the depths with cameras and lights, and used nets to bring an array of strange deep sea creatures to the surface. In his shipboard photography studio—outfitted with special aquariums and a powerful microscope—Zankl set out to capture the unique features and behaviors of these otherworldly organisms. This photo series offers rare glimpses of some of those creatures and the adaptations that enable them to survive and thrive in one of the planet’s most challenging environments.