The correct option is
D BeroeObelia, Jelly Fish and sea Anemone belong to the phylum Cnidaria. Obelia belongs to the class Hydrozoa it has a polypoid form and free swimming, sexual, medusoid form alternating with each other. Jellyfishes belong to the class Scyphozoa as they possess a large quantity of jelly-like mesoglea. They are solitary and medusoid in form. Sea anemones are sedentary and only polypoid in form and belong to the class Anthozoa.
So the correct answer is 'Beroe'.