King crabs are marine creatures with a unique anatomy. While many people might assume they have a similar number of legs to other crabs, king crabs possess a distinct arrangement that sets them apart. This difference often leads to questions about their true leg count and how they utilize these appendages.
The King Crab’s Leg Count
King crabs possess five pairs of legs, totaling ten appendages, though typically only eight are easily observed. These include three pairs of walking legs and one pair of chelipeds, their claws. The visible eight legs are primarily used for movement across the ocean floor.
The fifth pair of legs is much smaller and usually remains tucked away beneath the crab’s carapace. Because these smaller appendages are often hidden, they are less commonly noticed, contributing to the misconception about the king crab’s leg count. Despite being less prominent, this hidden pair plays several important roles.
The Specialized Functions of King Crab Legs
The visible appendages of a king crab each serve specific functions. The three pairs of walking legs are robust and enable the crab to move across diverse seafloor terrains. These legs are long and spidery, aiding in extensive migrations across the ocean bottom.
The first pair of legs consists of chelipeds, or claws. King crabs exhibit asymmetry in their claws; typically, one claw is larger and functions as a “crusher” for breaking open prey, while the smaller claw acts as a “pincer” or “cutter” for tearing food and delicate manipulation. These powerful claws are also used for defense and capturing prey.
The hidden fifth pair of legs, though small, performs crucial tasks. In female king crabs, these specialized appendages clean and aerate developing embryos, which they carry tucked under their abdomen. For males, this fifth pair assists in sperm transfer during mating.
King Crab Classification and Its Legs
The distinct leg count of king crabs is rooted in their evolutionary history and classification. King crabs belong to the family Lithodidae, placing them within the infraorder Anomura. This makes them more closely related to hermit crabs than to “true crabs” (infraorder Brachyura), which typically have four pairs of walking legs and one pair of chelipeds, all visible and used for locomotion.
The superficial resemblance of king crabs to true crabs, despite different evolutionary paths, is known as carcinization. This process describes how various crustacean groups have independently evolved crab-like body forms. The reduced fifth pair of legs, tucked beneath the body, is an anatomical feature supporting the king crab’s closer relationship to hermit crabs.