Grammatostomias flagellibarba is a species of deep-sea fish belonging to the family Opisthoproctidae, commonly known as barreleye fish. This species is notable for its unique adaptations to life in the dark depths of the ocean, including large, sensitive eyes that can detect faint light and a transparent head that allows for better vision of prey. The fish is primarily found in the deep waters of the Atlantic Ocean and Pacific Ocean. It typically inhabits depths ranging from 200 to 1,500 meters. Grammatostomias flagellibarba is characterized by its elongated body and long, filamentous barbels that help it sense its environment and locate food in the dark.