Which of the following is a characteristic of mollusks?

Mollusks are characterized as soft-bodied invertebrates, which distinguishes them from other types of animals. This group includes a diverse range of species such as snails, clams, and octopuses, all sharing the foundational trait of having soft bodies. Many mollusks also possess a hard external shell made of calcium carbonate, but this is not a requirement for classification as a mollusk.

The other options describe characteristics that do not fit within this category. Exoskeletons are typical of arthropods, which includes insects and crustaceans. Cold-blooded vertebrates refer to animals like reptiles and amphibians, which have a backbone and regulate their body temperature from the environment, while warm-blooded creatures, or endothermic animals, maintain a constant body temperature despite external conditions. Thus, the recognition that mollusks are soft-bodied invertebrates is essential in defining their biological classification.