King crabs are a popular seafood known for their impressive size and rich flavor. Despite their widespread recognition and crab-like appearance, these crustaceans are not actually classified as “true crabs.” This distinction stems from fundamental biological differences, which this article will explore.
What Defines a True Crab?
True crabs belong to the infraorder Brachyura, a scientific classification meaning “short-tailed.” These crustaceans typically possess ten limbs in total: two prominent claws, also called chelae, and eight walking legs, arranged as four pairs. The first pair of legs is usually modified into these powerful pincers used for defense, feeding, and even communication.
A distinguishing characteristic of true crabs is their abdomen, often referred to as a “tail.” This abdomen is significantly reduced and tucked tightly and symmetrically underneath their cephalothorax, which is the fused head and thorax of the animal. This hidden abdomen gives true crabs their characteristic broad, flattened, and often rounded or oval body shape. Their hard exoskeleton covers their entire body, providing protection.
King Crab’s Unique Anatomy and Lineage
King crabs exhibit several anatomical differences that set them apart from true crabs. While true crabs have eight walking legs and two claws, king crabs visibly possess only six walking legs, arranged in three pairs. A fourth, much smaller pair of legs is present but often tucked away within the gill chamber, making them less apparent.
The abdomen of a king crab is distinctly asymmetrical and does not tuck tightly or symmetrically under its body like that of a true crab. Instead, it is typically folded to one side. Taxonomically, king crabs belong to the family Lithodidae, part of the infraorder Anomura. This infraorder includes other crustaceans like hermit crabs and porcelain crabs, highlighting a different evolutionary lineage than true crabs (Brachyura).
The Story Behind the Name
The common name “king crab” reflects their impressive size and appearance rather than their strict scientific classification. Common names often serve descriptive purposes and do not always align with biological taxonomy. The use of “king” likely emphasizes their large stature and commercial value as a seafood item.
The crab-like appearance of king crabs, despite their different lineage, is a result of “carcinization.” This fascinating evolutionary process describes how various non-crab crustaceans independently develop a crab-like body form. King crabs have undergone this convergent evolution, developing a similar body plan to true crabs over time due to similar environmental pressures or lifestyles. This explains why they superficially resemble true crabs and have earned their familiar name.