Explain: Coelom.

(N/A) The body cavity,which is lined by mesoderm,is called the coelom. Animals possessing a coelom are called coelomates (e.g.,annelids,molluscs,arthropods,echinoderms,hemichordates,and chordates).
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. Such a body cavity is called a pseudocoelom,and the animals are called pseudocoelomates (e.g.,Aschelminthes).
The animals in which the body cavity is absent are called acoelomates (e.g.,Platyhelminthes).