Pseudocoelom: 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. Here body cavity is directly connected to the archenteron. Such a body cavity is called pseudocoelom and the animals possessing them are called pseudocoelomates. E.g.: Aschelminthes (Ascaris). Pseudocoelom is derived from blastocoel. The advantage of having a coelom is that a cavity filled with fluid around the organs provide a hydrostatic skeleton to aid movement and allow for more efficient circulation of nutrients and removal of wastes.