Acoelomorpha is a group of marine animals that are characterized by the absence of a coelom or body cavity. The word "acoelomorpha" itself has several synonyms, including Acoela, Platyhelminthes, and Turbellaria. Acoela refers to a subset of acoelomorpha, which includes small, flat, and worm-like animals that live in marine environments. Platyhelminthes is a broader category that includes all flatworms, many of which are parasitic. Turbellaria is another term for flatworms that refers to their ciliated, free-living forms. These synonyms are useful to use when discussing different aspects of acoelomorpha, such as their classification, taxonomy, and evolutionary history.