Q.Identify the structure that the archenteron becomes in a developing animal.

The coelom is the fluid-filled body cavity lying between the body wall and the alimentary canal, and whether an animal has one — and how it is lined — is one of the sharpest lines used to classify animals.

• Acoelomates have no body cavity; the space between body wall and gut is packed solid with mesoderm, restricting free movement of internal organs (e.g. flatworms).
• Pseudocoelomates have a body cavity that is only partly lined by mesoderm (formed as scattered pouches between ectoderm and endoderm), called a pseudocoel, filled with fluid that acts as a hydrostatic skeleton (e.g. roundworms/Aschelminthes). …