Are all seashells mollusks

Not all seashells belong to mollusks, but many do. Seashells are primarily made by marine animals within the phylum Mollusca, which includes snails, clams, and oysters. However, some other marine organisms, like certain types of crustaceans, can produce similar hard structures that resemble shells. So while mollusks are the primary producers of seashells, they are not the only organisms associated with shell-like formations.