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Relating to or inhabiting the layer of the water column of the open ocean that lies between the bathypelagic and hadopelagic layers at depths of about 4,000 to 6,000 meters (13,120 to 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.
(Physical Geography) referring to or occurring in the region of deep water above the floor of the ocean
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014