Chasmolithic refers to organisms that inhabit or thrive in deep, often dark, environments such as caves or deep-sea habitats. These species have adapted to extreme conditions, often exhibiting unique physiological traits, such as reduced eyesight or specialized feeding mechanisms. The term is derived from "chasm," meaning a deep fissure or cavity, and "lithic," relating to stone or rocky environments. Chasmolithic organisms contribute to our understanding of biodiversity and adaptation in extreme ecosystems.