Bilateria in which:- 1. A perivisceral coelom is characteristically present though it may be partly or wholly replaced by a perivisceral haemocoel. 2. There is no parenchyma, the organs usually being suspended in the coelom by folds of the coelomic epithelium. 3. Solenocytes may or may not be present in the excretory system, but flame cells are absent. 4. A blood vascular system is almost always present.