Which of the following is true about exoskeletons?

Exoskeletons are supportive structures found on the outside of an organism's body, primarily in arthropods such as insects, crustaceans, and arachnids. The correct assertion regarding exoskeletons highlights their ability to be shed periodically, a process known as molting. This shedding allows the organism to grow by replacing its old, rigid exoskeleton with a new, larger one.

During this process, the new exoskeleton forms underneath the old one before molting, enabling the organism to emerge with an exoskeleton that can accommodate its increased size. Additionally, exoskeletons provide vital muscle attachment points, enabling movement and function. This adaptability is crucial for the organism's growth and survival, as a rigid exoskeleton would limit growth potential and flexibility if it were not periodically updated.

The other options present misconceptions about exoskeletons. They do not cover the inside of the body, which is a characteristic of endoskeletons; they are not entirely rigid and capable of changing form; and they are not limited to mammals, as they are primarily found in arthropods and some other invertebrates.