What is an exoskeleton?

An exoskeleton is indeed characterized as a hard shell or casing that provides structural support and protection for an organism, typically found in invertebrates such as insects, crustaceans, and arachnids. It serves multiple functions, including defense against predators, preventing desiccation, and facilitating movement by acting as an anchor point for muscles. The material that makes up exoskeletons, often chitin, allows for both strength and flexibility, enabling the organism to navigate its environment effectively.

Other types of biological structures help with support, such as endoskeletons in vertebrates, but these are internal and involve bone or cartilage. Additionally, fluid-filled structures, like hydrostatic skeletons in some soft-bodied animals such as jellyfish, provide support in a different manner. Soft tissues can offer flexibility but do not provide the rigid support characteristic of exoskeletons. Hence, the definition encompassing a hard outer casing or shell is accurate for an exoskeleton.