Which structure is a defining characteristic of arthropods, allowing for growth and change?

The defining characteristic of arthropods that allows for growth and change is the exoskeleton. The exoskeleton is a hard outer structure made primarily of chitin that provides support and protection to the organism. As arthropods grow, they undergo a process called molting, during which they shed their old exoskeleton and form a new, larger one. This characteristic is vital because it enables arthropods to increase in size while maintaining the structural integrity required for mobility and survival in their environments.

In contrast, an endoskeleton, commonly found in vertebrates, does not allow for the same method of growth seen in arthropods, as it is internal and offers support in a different manner. The skull, specifically part of the endoskeleton, does not relate to the growth and change characteristic of arthropods. A carapace, which is a specific type of shell found in certain crustaceans, does not encapsulate the broader category of characteristics exhibited by all arthropods and is not essential to the growth process like the overall exoskeleton is.