The correct option is D Coelom
A coelom or body cavity is a cavity lined by an epithelium derived from mesoderm. A coelom is a space between the gut tube (lined with endoderm) and the body wall (with its outer covering of ectoderm).
Coelenteron is the central gastric cavity of a coelenterate.
Pseudocoel is not lined with a well-defined mesodermal membrane.
Blastocoel is the fluid-filled region of a blastula.
Thus, the correct answer is option A.