True crabs, the Brachyura, have four pairs of walking legs behind the claws. King crabs have three visible pairs, plus a small fourth pair folded under the rear of the carapace where it helps clean the gills and, in females, tend the eggs. Their abdomen is also asymmetrical, a legacy of ancestors that lived coiled inside gastropod shells.
That asymmetry places king crabs in the Anomura, alongside hermit crabs and squat lobsters. The resemblance to true crabs is carcinisation, the repeated evolution of a broad flattened body with the abdomen tucked beneath, which has arisen independently several times among decapods. King crabs are the best-known case of a hermit crab lineage arriving at a crab-like form without becoming crabs.
A related misreading concerns the Barents Sea. Red king crabs there are not native; they were deliberately introduced from the North Pacific by Soviet scientists in the 1960s and have since spread along the Norwegian and Russian coasts, where they are managed simultaneously as a valuable fishery and an invasive species.