Q. Compared to platyhelminthes which physiological problems have the cylindrical body of nematodes brought? How was that problem solved?

The cylindrical shape of nematodes made impossible the respiration exclusively by simple diffusion among cells since there are tissues far from the external. This problem was solved by the presence of an internal cavity in the body filled with fluid, the pseudocoelom.

The pseudocoelom has the function of distributing nutrients and gases to the body and to collect residuals, besides serving as a hydrostatic base to keep the worm shape. For the fact that the pseudocoelom and the pseudocoelom fluid do not characterize a true circulatory system with blood and heart it is not said that in nematodes the respiration is cutaneous it is considered that these animals still make respiration by diffusion.