Every time scientists make a new discovery, they add that knowledge and correct their older discoveries accordingly.
The correct option is C, ROUND WORM is a pseudoceolomate. Pseudoceolomate have a body cavity surrounding the gut but the gut itself is not surrounded by mesoderm; generally, their body cavity are lined by mesoderm derived tissue on one side and endoderm derived tissue on the other side. Other examples of pseudoceolomate are hook worm, hair worm, rotifers and pinworm. They are mostly parasitic in nature.
