The correct option is D Sea anemone
Diploblastic animals have two cell layers to their bodies, an outer ectoderm and an inner endoderm. The phylum Cnidaria contains diploblastic animals.
Acoelomate animals have no true body cavity such as Porifera, Cnidaria, Ctenophora, Platyhelminthes, Mesozoa, Nemertina, Gnathostomulida.
Sea anemone is classified in the phylum Cnidaria and thus, is diploblastic acoelomate.
Thus, the correct answer is option D.