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Relating to or inhabiting the layer of the water column of the open ocean that lies below the abyssopelagic layer at depths greater than about 6,000 meters (19,680 feet).
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.