Pseudocoelomate metazoans have a fluid-filled body cavity, the pseudocoelom, which, unlike a true coelom, does not have a cellular peritoneal lining. Most of the pseudocoelomates (e.g., the classes Nematoda and Rotifera) are small and none possess an independent vascular system.

Is a pseudocoelom and coelom?

A pseudocoelom is a body cavity that lies between mesodermal and endodermal tissue and is, therefore, not completely surrounded by mesodermal tissue. A “true” coelom is completely surrounded by mesodermal tissue, and can thus be subdivided into compartments.

Why is a pseudocoelom considered to be a false coelom?

All triploblastic animals possess a coelom. ... A coelom is a true body cavity, whereas a pseudocoelom is a false coelom that is not fully functional. Only a coelom is fully lined with mesoderm tissue. Pseudocoeloms arose early in animal evolution and evolved into coeloms.