Animals in which the body cavity is not lined by mesoderm, and instead, the mesoderm is present as scattered pouches in between the ectoderm and endoderm are:

The correct option is B

Pseudocoelomates

Body cavity is the cavity present between body wall and gut wall. In some animals, the body cavity is not lined by mesoderm. Instead, the mesoderm is present as scattered pouches in between the ectoderm and endoderm. This type of a body cavity is called a pseudocoelom, and the animals possessing it are called pseudocoelomates. Species belonging to phylum Aschelminthes exhibit this type of body cavity.