Some members of this phylum have ptychocysts, which help create tubes, and several others possess a tube called the actinopharynx, leading into the body cavity. Its classes include Anthozoa and Cubozoa, and the two germ layers of its members are separated by a fluid called mesoglea. Their life cycles often include the sessile polyp and mobile medusa stages, and structures characteristic of them are nematocytes, or stinging cells. For 10 points, name this radially-symmetric phylum which includes 
Some members of this phylum have ptychocysts, which help create tubes, and several others possess a tube called the actinopharynx, leading into the body cavity. Its classes include Anthozoa and Cubozoa, and the two germ layers of its members are separated by a fluid called mesoglea. Their life cycles often include the sessile polyp and mobile medusa stages, and structures characteristic of them are nematocytes, or stinging cells. For 10 points, name this radially-symmetric phylum which includes hydrozoa, anemones, and jellyfish.
Some members of this phylum have ptychocysts, which help create tubes, and several others possess a tube called the actinopharynx, leading into the body cavity.
Cnidaria [the "c" is silent, but be lenient with pronunciation]