Question

1- What does the coelom substitute/replace?

2- What are epithelial cells often modified into?  

Answer 1

1.The coelom substitutes /replaces the circulatory system/blood vascular apparatus.With increase in body size of primitive diploblastic and triploblastic animals, the body weight also increases as a result of which stress is laid on the differemt body organs as the animals move thereby preventing the formation of circulatory system that could be effective.

2.Epithelial cells are often modified into goblet cells in stomach that secrete mucus.They are also modified to form microvilli that functions in absorption,secretion,cell adhesion etc.