Body Cavity or Coelom

Classification of Animals Non Chordates of Class 11

The fluid filled space between the gut and the outer body wall is a body cavity. On the basis of development, it is of following types:

1. Acoelomates – The animals without coelom or body cavity are called a coelomates. e.g. Cnidarians, flatworms (platyhelminthes).

Fig. Different patterns of embryonic developments as found in pseudocoelomates, protostomes and deuterostomes

2. Pseudocoelom – The body cavity between the gut and body wall is not lined by mesoderm (Peritoneum) e.g. Nemathelminthes (Ascaris).

3. Eucoelom – The body cavity lined from all sides by mesodermal peritoneum.

(a) Schizocoel – formed by the splitting of mesodermal band. e.g. Annelids, Arthropods, Molluscs.

(b) Enterocoel – formed from the pouches of the archenterons or primitive gut e.g. Echinoderms and chordates.