Having a coelom formed from a mesodermal pouch off the primitive gut.

Enterocoelous development is the stage of embryological development of deuterostomes in which the coelom forms. The stage starts with the gastrula; as the archenteron forms, pockets of migrating cells also form, creating another layer between the endoderm and ectoderm, the mesoderm. These pockets gradually expand to form the coelom.