FlatWorm

The flatworms, or Platyhelminthes, Plathelminthes, or platyhelminths (from the Greek platy, meaning "flat" and , helminth, meaning "worm") are a phylum of relatively simple bilaterian, unsegmented, soft-bodiedinvertebrates. Unlike other bilaterians, they are acoelomates (having no body cavity), and have no specialized circulatory andrespiratory organs, which restricts them to having flattened shapes that allow oxygen and nutrients to pass through their bodies by diffusion.

* The digestive cavity has only one opening for both the ingestion (intake of nutrients) and egestion (removal of undigested wastes); as a result, the food cannot be processed continuously.

* In traditional medicinal texts, Platyhelminthes are divided into Turbellaria, which are mostly non-parasitic animals such as planarians, and three entirely parasitic groups: Cestoda, Trematoda and Monogenea; however, since the turbellarians have since been proven not to be monophyletic, this classification is now deprecated.

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