Definition of Abyssopelagic zone.

The abyssal zone is the pelagic zone that contains the very deep benthic communities near the bottom of oceans. Abyss is from the Greek word meaning bottomless sea. At depths of 4,000 to 6,000 meters (13,123 to 19,685 feet), this zone remains in perpetual darkness and never receives daylight. Its permanent inhabitants – for example, the  Black swallower, tripod fish, deep-sea anglerfish, and the giant squid – are able to withstand the immense pressures of the ocean depths, up to 775  kilograms per square centimeter (76 megapascals or 4.92 long tons force per square inch). Many abyssal creatures have underslung jaws to sift through the sand to catch food. The deep trenches or fissures that plunge down thousands of feet below the ocean floor – for example, the midoceanic trenches such as the  Mariana Trench in the Pacific – are almost unexplored. Only the  bathyscaph Trieste has been able to descend to these depths. These regions are also characterized by continuous cold and lack of nutrients. The abyssal zone has temperatures around 2 to 3 degrees Celsius.

The pelagic zone is the part of the open sea or ocean that is not near the coast. In contrast, the neritic zone comprises the water that is near to (and is significantly affected by) the coast or the continental shelf. The name is derived from the Greek πέλαγος (pélagos), which might be roughly translated as "sea" but is more accurately translated as "open sea." When used on its own, "pelagic" describes something that exists in the open sea as opposed to inland or coastal waters.