Pseudocoeloma

Pseudocoeloma is a term used in zoology to describe a body cavity that is not completely lined by mesoderm. It is a type of body cavity found in certain groups of invertebrates, notably nematodes, rotifers, and acanthocephalans. This cavity, also referred to as a blastocoel, is a remnant of the embryonic blastocoel, the fluid-filled space within the blastula.

Unlike a true coelom, which is entirely surrounded by mesoderm-derived tissues, the pseudocoelom is only partially enclosed by mesodermal tissue. The gut, which is derived from the endoderm, lies within this space, and the outer layer of the body wall is derived from ectoderm. The mesoderm forms a layer of cells that lies between the ectoderm and the endoderm, but it does not fully envelop the internal organs.

The presence of a pseudocoelom has significant implications for the physiology and locomotion of these animals. It acts as a hydrostatic skeleton, allowing for movement through muscular contractions that push against the fluid-filled cavity. This fluid also plays a role in the distribution of nutrients and waste products within the organism. The pseudocoelom is a defining characteristic of the pseudocoelomate phyla, distinguishing them from animals with true coeloms (coelomates) and those with no body cavity (acoelomates).