Shellfish as a noun is an aquatic invertebrate, such as a mollusc or crustacean, that has a shell. while Mollusk as a noun is a soft-bodied invertebrate of the phylum mollusca, typically with a hard shell of one or more pieces.
Part of speech: noun
Definition: An aquatic invertebrate, such as a mollusc or crustacean, that has a shell.
Part of speech: noun
Definition: A soft-bodied invertebrate of the phylum Mollusca, typically with a hard shell of one or more pieces.
We hope you now know whether to use Shellfish or Mollusk in your sentence.