Eumetazoa is a major division of the animal kingdom comprising all multicellular forms except the sponges. It is a large group including most of the multicellular animals. Hence it is subdivided further into two groups.
- Diploblastic animals – having ectoderm and endoderm as two layers in the body wall. Ex: Coelenterata. Diploblastic organisms are organisms which evolve from such an ovum and include cnidaria and ctenophores.
- Triploblastic animals – having ectoderm, mesoderm, and endoderm as three layers in the body wall. Triploblasty is a condition of the blastula in which there are three primary germ layers: the ectoderm, mesoderm, and endoderm.
The Triploblastic animals are further divided into three groups based on the presence or absence of an embryonic body cavity called coelom.
- Acoelomata – no coelom Ex: Platyhelminthes
- Pseudocoelomata – with a false coelom Ex: Nematoda
- Coelomata – with a true coelom
