ectoskeleton

An exoskeleton is an external skeleton that supports and protects an animal's body. It is a rigid outer covering that can be shed and regrown, a process called molting, to allow for growth. Exoskeletons are found in many invertebrates, including insects, arachnids, crustaceans, and some other arthropods.

The exoskeleton is composed primarily of chitin, a tough polysaccharide, often strengthened with proteins and minerals like calcium carbonate. This structure provides several advantages, including protection from predators and physical damage, support for the body's weight, and a surface for muscle attachment, enabling movement. It also helps to prevent desiccation, or drying out, in terrestrial environments.

The thickness and composition of the exoskeleton can vary greatly depending on the species and its environment. For instance, the shells of crustaceans are often heavily mineralized, providing substantial armor, while the exoskeletons of insects are typically lighter and more flexible.

Despite its benefits, an exoskeleton limits an organism's size, as its weight increases disproportionately with volume. Molting, while necessary for growth, leaves the animal vulnerable and energetically costly. The exoskeleton also restricts respiration in some cases, with many terrestrial arthropods relying on specialized tracheal systems for gas exchange. The study of exoskeletons is a significant part of understanding invertebrate anatomy and evolution.