Definition of "flatworm" [flat•worm]

• Any of various parasitic and nonparasitic worms of the phylum Platyhelminthes, such as a tapeworm or a planarian, characteristically having a soft, flat, bilaterally symmetrical body and no body cavity. Also called platyhelminth. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Or of the Spirometra mansoni, commonly called a flatworm, which can grow up to fourteen inches long and take up residence in your brain, where it feeds upon your cerebral matter until you are reduced to a vegetative state?"
• "The flatworm is the simplest living multicellular animal to have bilateral symmetry, and its primeval ancestors must have been the first to develop this."
• "The color of the flatworm is a very dark brown and the stomach with a thin pale line."