mesozoan[mes′ə zō′ən, mez′-]
mesozoan definition by Webster's New World
Webster's New World College Dictionary Copyright © 2010 by Wiley Publishing, Inc., Cleveland, Ohio. Used by arrangement with John Wiley & Sons, Inc.
any of a phylum (Mesozoa) of small, multicellular, wormlike organisms characterized by a very simple, ciliated body with only a mouth, body cavity, and anus: it is a parasite in various marine invertebrates
mesozoan - Science Definition
Any of a variety of very small parasitic marine animals of the group Mesozoa. Mesozoans resemble worms and have simple bodies divided into two layers. The outer layer is covered with cilia, and there are no internal organs. The taxonomic status of the Mesozoa is unclear, as some scientists believe the mesozoans to be an ancient and primitive group and others regard them as degenerate forms of more complex animals.