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Any of various small wormlike animals that are parasites of marine invertebrates and have an inner layer of one or more cells surrounded by an outer layer of ciliated cells.
[From New Latin Mesozōa, former phylum name : meso- (because the animals were considered to be intermediate between the protozoans and the metazoans in structure) + -zōa, pl. of -zōon, animal; see -zoon.]
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.
(Animals) any of several wormlike parasites of the group Mesozoa that live in marine vertebrates
Collins English Dictionary – Complete and Unabridged, 12th Edition 2014 © HarperCollins Publishers 1991, 1994, 1998, 2000, 2003, 2006, 2007, 2009, 2011, 2014