Aschelminthes (roundworms) are classified as pseudocoelomates because their body cavity is not lined by mesoderm, but instead contains mesoderm as scattered pouches . The other statements are incorrect: Molluscs and Arthropods (which include insects) are true coelomates, possessing a body cavity lined by mesoderm . Platyhelminthes (flatworms) are acoelomates, meaning they lack a body cavity . This specific question was a part of the AIPMT PRE 2010 examination .