SHELL: - Advantage: the shell can be a good protection against predators and it protects mollusks' soft body. - Disadvantage: the shell can be heavy and a lot of energy is needed to move it which can slow down a mollusk
SPINY SKELETON: - Advantages: spiny skeleton serves as a protection against predators. - Disadvantages: in some species, spine skeletons do not allow for much body flexibility.
