The snow crab (Chionoecetes opilio) is a commercially harvested species found in the cold, deep waters of the North Atlantic and North Pacific Oceans. Also known as the Queen crab, this crustacean is recognized for its delicate meat and long, slender limbs. It prefers muddy and sandy bottoms on the continental shelf and slope, where water temperatures remain consistently low, often between -1 and 5 degrees Celsius.
Key Characteristics of the Carapace and Coloration
The main body shell, or carapace, is relatively flat and appears rounded or somewhat heart-shaped when viewed from above. The shell surface is granulated, featuring small bumps or spines that provide a rough texture. This hard exoskeleton offers protection and anchors the crab’s powerful leg muscles.
The snow crab’s coloration serves as camouflage against the dark ocean floor. The dorsal side (top of the shell) typically ranges from light tan to brownish-red, occasionally displaying a slightly iridescent quality. Conversely, the underside, including the belly and feet, is notably lighter, often appearing pale yellow or creamy white.
Dimensions and Distinctive Limb Structure
The most recognizable feature of the snow crab is its disproportionately long and thin limbs, often described as “spidery.” Like all decapods, the snow crab possesses five pairs of appendages attached to the cephalothorax, totaling ten limbs. This includes eight long walking legs and two specialized front appendages called chelipeds.
The walking legs are the source of the crab’s high meat yield and can span a distance far exceeding the carapace width. A large male may have a carapace width up to 16.5 centimeters, but the leg span can reach approximately 90 centimeters. The chelipeds (claws) are present on the first pair of appendages but are typically smaller and less massive compared to those of other large crab species.
Distinguishing Males from Females
A pronounced difference in size and body structure exists between male and female snow crabs, a trait known as sexual dimorphism. Mature males are considerably larger than females, often growing nearly twice as large in carapace width and reaching greater overall weights. Commercially harvested males typically weigh between 0.5 and 1.35 kilograms, while females generally weigh around 0.5 kilograms.
The most reliable way to differentiate the sexes is by observing the abdominal flap, which is folded underneath the main body shell. Males have a narrow, distinctly triangular flap that fits snugly between the rear walking legs. Females possess a much wider, more rounded abdominal flap, adapted to hold and protect the egg mass during reproduction.
Visual Differences from Similar Crabs
Snow crabs are often confused with other commercially important crustaceans, particularly the King Crab and the closely related Tanner Crab. The primary distinction between the Snow Crab and the King Crab is the total number of legs. Snow crabs belong to the “true crab” group, having four pairs of walking legs plus two claws, totaling ten appendages.
King Crabs, such as the Red King Crab, are not true crabs and only have three pairs of walking legs plus two claws, totaling eight appendages. King Crabs are also much larger and heavier, with a spikier, more ornate carapace and notably thicker legs that do not break as easily as the Snow Crab’s slender limbs. Differentiating the Snow Crab (Chionoecetes opilio) from the Tanner Crab (Chionoecetes bairdi) is more subtle, as they are members of the same genus.
Tanner crabs are generally larger than snow crabs and tend to have a carapace that is wider relative to its length, giving it a more circular appearance. The snow crab’s carapace is typically less wide and can appear slightly more triangular. Furthermore, the two species are known to hybridize in the Bering Sea, sometimes making visual identification challenging even for experts, as hybrids exhibit intermediate physical characteristics.