Mesopelagic

Part of speech: adjective

Definitions

1. the ocean zone located between approximately 200 and 1000 meters depth, characterized by minimal sunlight penetration and inhabited by creatures adapted to dim lighting conditions
2. a distinct layer of the ocean situated at depths ranging from around 200 to 1000 meters, featuring scarce light and a unique ecosystem of organisms suited for low-light environments
3. an intermediate division of the ocean that extends roughly from 200 to 1000 meters deep, where light is minimal and life forms are specifically adapted to twilight conditions

Etymology: Ocean scientists needed a name for the twilight layer of water that sits below the sunlit surface but above the deep, pitch-black abyss, and they built it from two Greek pieces. The first, "mesos," means "middle," a word that also gave English "mesosphere" and "Mesopotamia" ("land between the rivers"). The second, "pelagic," comes from Greek "pelagos," "open sea," and describes life that lives in the open water rather than on the seabed or near the shore. Put together, "mesopelagic" simply means "middle open sea." It is a technical coinage rather than an ancient term: the ancient Greeks had no notion of this depth zone, and the word was formed in modern scientific English from classical roots to label a particular band of water roughly 200 to 1,000 metres down, where only faint light reaches. Many animals that live there, such as lanternfish, migrate up toward the surface at night to feed.