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. Make sure the children understand about these animals.
Arthropods are the largest group of animals.
Arthropod means jointed feet. They include insects, crustaceans, and spider relatives. Echinoderm means spiny skin. Even through echinoderms are called invertebrates, they do seem to have an internal skeleton of calcium plates. They also all have a five part body, a water vascular system and structures called tube feet.