pseudocoelem

A pseudocoelom is a fluid-filled body cavity that is not completely lined by mesoderm. It is a characteristic feature of pseudocoelomates, a group of invertebrates that includes nematodes, rotifers, and some other phyla. The pseudocoelom is formed during embryonic development and is a space between the digestive tract and the outer body wall.

The pseudocoelom plays a vital role in the physiology of pseudocoelomates. It acts as a hydrostatic skeleton, providing support and enabling locomotion. The fluid within the pseudocoelom can also help in the circulation of nutrients and waste products, as well as in gas exchange. Furthermore, the pseudocoelom can house internal organs and protect them from mechanical damage.

The presence or absence of a true coelom, which is a body cavity completely surrounded by mesoderm, is a significant characteristic used in classifying animals. Animals with a true coelom are called coelomates, while those with a pseudocoelom are pseudocoelomates. Invertebrates lacking any body cavity are called acoelomates. The distinction between these body cavity types is fundamental to understanding animal evolutionary relationships. Pseudocoelomates represent an evolutionary grade between acoelomates and coelomates, showcasing a step in the development of more complex body plans.