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. You can work with the folders containing the classes of these three phyla. This is enough work for one day.