The correct option is D Echinodermata
In Echinodermata, enterocoeles development begins once the embryo reaches the gastrula phase of development. The mesoderm begins to form as pockets like structure via folding of the endoderm. When the pockets of cells meet, the mesoderm is formed. A complete layer of tissue right in between the endoderm and ectoderm layers. This then leads to the formation of a coelom.
So, the correct answer is option A.