What is coelom? Describe its types.

(N/A) The body cavity,which is lined by mesoderm,is called coelom. The presence or absence of coelom is very important in animal classification.
Based on the presence or absence of coelom,animals are classified into three groups:
$1$. Acoelomate: Animals in which the body cavity is absent are called acoelomates. Examples include Porifera,Platyhelminthes,Coelenterata,and Ctenophora.
$2$. Pseudocoelomate: 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 possessing them are called pseudocoelomates (e.g.,Aschelminthes).
$3$. Coelomate: Animals possessing a true coelom (body cavity lined by mesoderm on all sides) are called coelomates. Examples include Annelida,Mollusca,Arthropoda,Echinodermata,Hemichordata,and Chordata.