The correct option is C Mesoglea
Hydra is diploblastic organism. The outer layer of hydra is epidermis while the inner layer is gastrodermis. These layers are separated by mesoglea. Mesoglea is non-living, jelly-like substance found between the two epithelial cell layers. The mesoglea serves an internal skeleton or endoskeleton, supporting the body.
Thus, the correct answer is option C.