includes Class Anthozoa ( corals and sea anemones ), Class Hydrozoa ( hydrozoans ), Subphylum Medusozoa: Class Cubozoa ( box jellyfish ), Class Scyphozoa ( jellyfish ), and Class Staurozoa which contains Order Stauromedusae ( stalked jellyfish ). Phylum Cnidaria may also contain Family Polypodiidae and Family Tetraplatidae . Species in