Do members of phylum Cnidaria have a mesoderm layer?

Question

are all animals (with the exception of sponges) supposed to have a mesoderm, endoderm, and exoderm?

Thanks a lot

Answer 1

No.

Cnidaria and Ctenofora are diploblasts.  They only have 2 germ layers.  The endoderm and the ectoderm.  Whereas triploblasts have all three layers.  And poriferans(sponges) have no germ layers.