Body Organization- Germ layers

Germ Layers in the embryo-Diploblastic and Triploblastic animals.

Q: How do germ layers are formed and what would they become in later development?

1. In all the eumetazoans animals (all multicellular animals except parazoans- sponges), during embryonic development, the embryo forms germ layers during gastrulation. Yet, Sponges do not develop any germ layers, even though gastrulation occurs.
2. In the case of triploblastic animals (Platyheminthes to Chordates), 3 germ layers are formed during the gastrulation (ectoderm, endoderm and mesoderm).
3. Whereas in diploblastic animals, in coelenterates, only two germ layers (ectoderm, endoderm) are formed, but the third layer (mesoderm) is not formed, hence they are diploblastic.
4. Video– germ layers formation in Diplo & triploblastic- organogenesis.
5. Q: Do the sponges and coelenterates show body organs?
6. No. Because mesoderm is not formed.