Platyhelminths, commonly known as flatworms, are a diverse group of organisms that are found in both marine and freshwater environments. They are characterized by their flattened bodies, lack of segmentation, and simple nervous system. There are numerous synonyms for the word Platyhelminths, including Nemertea, which refers specifically to ribbon worms, and Acoelomorpha, which includes a group of marine flatworms. Other synonyms include Turbellaria, which encompasses free-living flatworms, and Trematoda, which includes parasitic flatworms such as liver flukes. Additionally, Cestoda is another synonym that refers specifically to tapeworms, which are parasitic in nature and consist of a long chain of segments.