What is a defining feature of crustaceans’ anatomy?

Crustaceans are uniquely characterized by their exoskeleton, which is a hard outer covering made primarily of chitin and often contains calcium carbonate. This exoskeleton provides structural support and protection against predators and environmental conditions. The combination of chitin and calcium contributes to the strength and durability of their body structure, differentiating them from other marine organisms that may have soft bodies or different types of protective covering.

The exoskeleton also plays a significant role in the process of molting, allowing crustaceans to grow by shedding their old exoskeleton and forming a new, larger one. This adaptation is crucial to their life cycle and growth, further emphasizing the importance of this feature in their anatomy.

The other options present features not aligned with the defining characteristics of crustaceans, helping to clarify the unique anatomical structure that distinguishes them in the marine environment.