Which phylum is commonly described as flatworms?

Which phylum is commonly described as flatworms?

• A. Platyhelminthes
• B. Nematoda
• C. Annelida
• D. Echinodermata

Answer: (A)

Flatworms are identified by their dorsoventrally flattened bodies and lack of a true body cavity (acoelomate). This flat, simple design is the defining feature of the phylum Platyhelminthes, which includes both free-living forms like planarians and many parasitic species such as flukes and tapeworms. Because the body is so thin, gases and nutrients can diffuse directly with the surrounding environment, so they don’t need a specialized circulatory or respiratory system. The other groups differ in their body plans: roundworms have a tubular, cylindrical shape with a false coelom (pseudocoelom); segmented worms have a true coelom and body segmentation; and echinoderms show radial symmetry and a distinct water vascular system. So the phylum commonly described as flatworms is Platyhelminthes.

Flatworms are identified by their dorsoventrally flattened bodies and lack of a true body cavity (acoelomate). This flat, simple design is the defining feature of the phylum Platyhelminthes, which includes both free-living forms like planarians and many parasitic species such as flukes and tapeworms. Because the body is so thin, gases and nutrients can diffuse directly with the surrounding environment, so they don’t need a specialized circulatory or respiratory system. The other groups differ in their body plans: roundworms have a tubular, cylindrical shape with a false coelom (pseudocoelom); segmented worms have a true coelom and body segmentation; and echinoderms show radial symmetry and a distinct water vascular system. So the phylum commonly described as flatworms is Platyhelminthes.