EVERYDAY SCIENCE

Detailed explanation-1: -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.

Detailed explanation-2: -Coelomates (also known as eucoelomates–"true coelom") have a fluid filled body cavity called a coelom (pronounced /ˈsiːləm/) with a complete lining called peritoneum derived from mesoderm (one of the three primary tissue layers).

Detailed explanation-3: -Pseudocoelomates are animals with a fluid-filled body cavity not completely lined with mesoderm tissue. The cavity is in between the mesoderm and the endoderm and is called a pseudocoelom (Fig. 3.17 B). The roundworms (phylum Nematoda) are examples of pseudocoelomates.

Detailed explanation-4: -During the development of pseudocoelomates, mesoderm occupies only a part of blastocoel adjoining the ectoderm. The blastcoel or segmentation cavity fails to disappear in the adult. It persists in the adult in between the body wall and the alimentary canal in the form of ‘pseudocoelom’.

Detailed explanation-5: -Coelomates are organisms with a mesodermally lined body cavity, pseudocoelomates are organisms with patches of mesoderm on their body cavity, and acoelomates are organisms with no body cavity at all.