Organisms of the mesopelagic zone are characterized by

Bioluminescence and large sensitive eyes

The Mesopelagic zone is a range of ocean depth that starts from 650 feet below the water's surface to around 3,280 feet below. Light penetrations from the surface of the ocean nearly disperse at this area. The most common organisms found in the mesopelagic zone are small fish, squid, and simple shellfish. Organisms of the mesopelagic zone are characterized by bioluminescence and large sensitive eyes. Their large eyes are capable of detecting light only 1% as intense as that visible to the human eye and majority of the organisms have light producing organs that give off a phosphorescence that makes them glow in the dark.