Hydras, Corals, Jelly fish, and Sea anemones are Cnidaria. When you think about a worm, you think about earthworms. Planarians and tapeworms are examples of Platyhelminthes. Tricinella and hookworms are example of round worms. Earthworms and leeches and seaworms are examples of segmented worms.
Mollusks are soft-bodied invertebrates.
They have a thick, muscular foot. Some mollusks have a shell. All mollusks have a soft mantle which covers most of its body. The mantle produces the materials which make up the shell. At this point, you should do a three period lesson on the animals.