Question

What is the relationship between germinal layers and the formation of body cavity in case of coelomates, acoelomates and pseudocoelomates?

Answer 1

Germ layers:

Ectoderm, mesoderm and endoderm are the germ layers which arise during the embryo formation. These layers give rise to all the tissues/ organs of the fully formed individuals.

Diploblastic and triploblastic organisms:

Depending upon the number of germ layers, organisms are of two types:

● Diploblastic organisms: Having two germ layers

● Triploblastic organisms: Having three germ layers

Coelom and germ layers:

The cavity between the body wall and the gut wall (wall of the digestive tract) is known as coelom.

● Diploblastic animals lack coelom and are called acoelomates.

● Triploblastic organisms possess coelom. Depending on the nature of their coelom, they are classified into the following:

○ Pseudocoelomates

○ Eucoelomates

Phyla depending on the nature of their coelom:

Category	Characteristic	Possible phylum/ phyla
Acoelomates	Organism without any body cavity between body wall and gut wall.	Platyhelminthes
Pseudocoelomates	Body cavity is not lined by mesoderm. Mesoderm is present as scattered pouches in between the ectoderm and endoderm.	Aschelminthes
Coelomates	Body cavity arises as a cavity or pouchings of the embryonic membrane and is lined by mesoderm on all sides.	Annelida, Arthopoda, Mollusca, Echinodermata, Hemichordata and Chordata