Hermit crabs are crustaceans known for inhabiting discarded shells. A common question people often have about them relates to their distinctive anatomy, particularly the number of appendages they possess, which contributes to their unique way of life.
The Visible Walking Legs
Hermit crabs typically present three pairs of visible appendages. The most prominent pair consists of the chelipeds, commonly known as claws. These modified legs serve multiple purposes, including defense against predators, manipulating food for consumption, and aiding in climbing various surfaces.
Following the chelipeds are the second and third pairs of walking legs. These are primarily responsible for the crab’s locomotion, enabling it to move across the substrate and navigate its surroundings. They also provide balance, which is particularly important as the crab carries its shell, and assist in climbing to find food or escape danger.
The Hidden Appendages
Beyond the easily observed limbs, hermit crabs possess additional pairs of smaller appendages, often tucked away. These hidden legs are crucial for the crab’s survival.
The fourth pair of legs is typically smaller than the walking legs and is usually kept within the shell. These smaller appendages are specialized for holding the shell securely onto the crab’s soft, unprotected abdomen. Without this crucial grip, the hermit crab would easily lose its protective home.
The fifth and final pair of legs is even more diminutive and is often located near the gills. These minute appendages are used for cleaning and maintaining the gills, ensuring proper respiration within the shell.
Why the Leg Count Can Be Confusing
The exact number of legs a hermit crab has can be confusing because not all of its appendages are equally visible or used for locomotion.
When people first encounter a hermit crab, they typically notice only the larger, more active walking legs and the prominent claws. This leads to an incomplete count based solely on what is immediately apparent.
The smaller, hidden pairs of legs are often tucked away inside the shell or are simply so small that they are difficult to discern without close inspection. While different species of hermit crabs share the same general leg structure, slight variations in leg size or appearance among them can further contribute to the confusion. Despite only a few pairs being visible, hermit crabs are equipped with ten legs, each serving a specific purpose.