The Macropinna microstoma, commonly known as the barreleye fish, is found in the deep sea. It has a transparent head, tubular eyes, and a unique ability to rotate its eyes to look upward. This fish inhabits the mesopelagic zone and feeds on zooplankton and jellyfish.

Macropinna microstoma, commonly known as the barreleye fish, is native to the deep ocean waters of the Pacific Ocean. Its distribution includes the temperate and tropical regions of the Pacific, particularly off the coasts of California and Baja California in the United States, as well as other areas within the North and Central Pacific Ocean.

This species inhabits the mesopelagic zone of the ocean, commonly known as the 'twilight zone,' at depths ranging from 400 to 2,500 feet (about 120 to 760 meters). The environment is characterized by low light conditions, cold temperatures, and high pressure. The water temperature in this zone typically ranges from 4 to 5 degrees Celsius.

Macropinna microstoma occupies a specialized ecological niche where it primarily feeds on zooplankton and small jellyfish. The fish's transparent head and upward-facing tubular eyes are adaptations that allow it to better detect prey and navigate the dimly lit environment. This unique adaptation helps it to gather light from above and see silhouettes of prey items. The barreleye fish is an important part of the deep-sea food web, contributing to the biodiversity of the mesopelagic zone.