Differences: 1. The roundworm has a body cavity called a coelom. It is a false coelom (pseudocoelom) because it is not completely lined with mesoderm tissue. A flatworm has no body cavity and is called an “acoelomate”.Click to see full answer. Consequently, do roundworms have a body cavity?Unlike the flatworms, the roundworms have a body cavity with internal organs. A roundworm has a complete digestive system, which includes both a mouth and an anus. This is a significant difference from the incomplete digestive system of flatworms.One may also ask, what type of Coelom do roundworms have? Type of body cavity (coelom): Flatworms are acoelomate – they have three germ layers, but no coelom. Roundworms are pseudocoelomate – they have a cavity that forms between the mesoderm and the endoderm. Segmented worms are coelomate – they have a true coelom which forms within the mesoderm. Moreover, what is the body cavity of a roundworm called? The pseudocoelom is a fluid-filled body cavity lying inside the external body wall of the nematode that bathes the internal organs, including the alimentary system and the reproductive system (PeriFIG 1).What type of body cavity does Ascaris have? Ascaris Body Cavity A spacious fluid filled cavity is present between the body wall and the visceral organs. The fluid filled cavity is called as pseudo coelom and it cannot be considered as the true coelom as, It is not lined by the coelomic epithelium. It also has no relation with the reproductive and excretory