Answer:
A diploblast has no mesoderm.
A pseudocoelom has the same functions as a true coelom. In a coelomate, the tissue lining the inner side of the body cavity arises from the same germ layer as the tissue lining the outer side of the body cavity.
Explanation:
Diploblast organisms are the ones that have only two primary germ layers. These organisms have outer ectoderm and inner endoderm but no mesoderm. Example: Cnidarians
A true coelom is derived from mesoderm and is completely lined with tissue derived from mesoderm. The outer and inner linings of the coelom are made of muscle layers that are developed from the mesoderm.
A pseudocoelom is the one that is incompletely lined with mesoderm. Both pseudocoelom and a true coelom serve as shock absorber and provide space wherein the internal organs can be placed. The fluid present in them sere as medium for transport of nutrients, gases, etc.