Question

How useful is the study of the nature of body cavity and coelom in the classification of animals?

Answer 1

Coelom is a fluid filled space between the body wall and digestive tract. The presence or absence of body cavity or coelom, plays a very important role in the classification of animals. Animals that possess a fluid filled cavity between body wall and digestive tract are known as coelomates. Annelids, mollusks, arthropods, echinodermates, and chordates are examples of coelomates. On the other hand, animals in which the body cavity is not lined by mesoderm are known as pseudocoelomates. In such animals, mesoderm is scattered between the ectoderm and endoderm. Aschelminthes is an example of a pseudocoelomate. In certain animals, the body cavity is absent. They are known as acoelomates. An example of acoelomates is platyhelminthes

Answer 2

1. Organisms can be classified according to the presence or absence of the coelom. The body cavity, which is lined by mesoderm, is called the coelom. Animals possessing coelom are called coelomates, e.g., annelids, molluscs, arthropods, echinoderms, hemichordates, and chordates.
2. 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.
3. Such a body cavity is called pseudocoelom and the animals possessing it are called pseudocoelomates, e.g., aschelminthes. In pseudocoelomates, the body cavity is derived from the blastocoel of the embryo.
4. The animals in which the body cavity is absent are called acoelomates, e.g., platyhelminthes.