Question

Define haemocoel and true coelom.

Answer 1

Haemocoel arises in early development, but later it is almost completely obliterated by a greatly enlarged blastocoel. The blastocoel consists of sinuses filled with blood. Blood flows through this cavity and bathes the internal organs. Gonads are never differentiated from the haemocoel wall, and the coelom is confined to the cavities of excretory organs and ducts only.

On the other hand, the true coelom originates by a split within the embryonic mesoderm. The cavity of the coelom is thus bounded by a lining of mesodermal cells called peritoneum. The coelomic cavity is filled with coelomic fluid.