Which statement best describes a mollusk?

Which statement best describes a mollusk?

• A. A vertebrate with a backbone.
• B. An insect with wings.
• C. A soft-bodied invertebrate animal, often with a hard shell.
• D. A marine mammal.

Answer: (C)

Mollusks are soft-bodied invertebrates, often with a hard shell. This captures the essential traits: they lack a backbone, and many have a protective shell, like snails and clams. Some groups, such as octopuses and squids, don’t have an external shell, but they still share other defining features of mollusks, such as a muscular foot and a mantle. The combination of being invertebrate and typically having a shell makes this description the best fit. In contrast, a vertebrate with a backbone describes animals with spinal columns, like fish, birds, and mammals; an insect with wings describes a different phylum with a distinct body plan; and a marine mammal is a vertebrate that lives in the sea, not a mollusk.

Mollusks are soft-bodied invertebrates, often with a hard shell. This captures the essential traits: they lack a backbone, and many have a protective shell, like snails and clams. Some groups, such as octopuses and squids, don’t have an external shell, but they still share other defining features of mollusks, such as a muscular foot and a mantle. The combination of being invertebrate and typically having a shell makes this description the best fit.

In contrast, a vertebrate with a backbone describes animals with spinal columns, like fish, birds, and mammals; an insect with wings describes a different phylum with a distinct body plan; and a marine mammal is a vertebrate that lives in the sea, not a mollusk.