The below mentioned article provides biology notes on Eucoelomates.
The animals which possess true coelom are called eucoelomates or coelomates. The true eucoelomates is a body cavity which arises as a cavity in embryonic mesoderm. In this case, the mesoderm of the embryo provides a cellular lining, called coelomic epithelium or peritoneum, to the cavity.
The eucoelomates is filled with coelomic fluid secreted by the peritoneum. True coelum is found in annelids, echinoderms and chordates. True eucoelomates is of two types; schizocoelom (schizocoel) and enterocoelom (enterocoel).
It develops as a split in the mesoderm sheet. It is found in annelids, arthropods, molluscs.
The mesoderm arises from the wall of the embryonic gut or enteron as hollow outgrowths which form this type of coelom. It occurs in echinoderms and chordates. The cavity filled with blood is called haemocoel. It is found in arthropods and molluscs.