Final answer:
Clams, snails, sea slugs, and octopuses are part of the phylum Mollusca, which is a diverse group of invertebrates that usually have a hard shell, a mantle, and a radula.
Step-by-step explanation:
Clams, snails, sea slugs, and octopuses all belong to the phylum Mollusca. This is a highly diverse group of invertebrates that includes a variety of species, from terrestrial to marine environments. Mollusks are known for having a hard shell, a mantle, and a specialized feeding organ called a radula, although the manifestation of these features can vary greatly among the different classes within the phylum. For example, cephalopods such as octopuses and squids have a highly reduced shell. The classification of Mollusca includes seven classes: Aplacophora, Monoplacophora, Polyplacophora, Bivalvia, Gastropoda, Cephalopoda, and Scaphopoda.