King crabs are generally thought to be derived from hermit crab-like ancestors, which may explain the asymmetry still found in the adult forms. Although some doubt still exists about this theory, king crabs are the most widely quoted example of carcinisation among the Decapoda. The evidence for this explanation comes from the asymmetry of the king crab's abdomen, which is thought to reflect the asymmetry of hermit crabs, which must fit into a spiralshell. Although formerly classified among the hermit crabs in the superfamily Paguroidea, king crabs are now placed in a separate superfamily, Lithodoidea.
The golden king crab, Lithodes aequispinus, is caught in the Aleutian Chain off the coast of Alaska. The golden king crab is significantly smaller than the red and blue king crabs, averaging 5–8 pounds (2.3–3.6 kg). It tastes similar to the red and blue king crabs, though perhaps somewhat sweeter. They are considerably cheaper due to their appearance and size.
Lithodes maja occurs in the NorthAtlantic, including Northern Europe and Canada's east coast. It is not abundant enough to support commercial fishery, and is becoming rare in some areas.
In 2011, the scientists have found Neolithodes yaldwini on the edge of Antarctica, probably as a result of global warming, with major impacts on sediment texture, bioturbation and local faunal diversity.
Red (P. camtschaticus) and blue (P. platypus) king crabs are some of the most important fisheries in Alaska, however populations have fluctuated in the past 25 years and some areas are currently closed due to overfishing. The two species are similar in size, shape and life history. Habitat is the main factor separating the range of blue and red king crabs in the Bering Sea. Red king crabs prefer shallow, muddy or sandy habitats in Bristol Bay and Norton Sound, while blue king crabs prefer the deeper areas made up of cobble, gravel and rock that occur around the Pribilof, St. Matthew, St. Lawrence and the Diomede Islands.
Red king crabs have an 11-month brood cycle in their first reproductive year and a 12 month cycle thereafter. Both red and blue king crabs have planktotrophic larvae that undergo 4 zoeal stages in the water column and a non-feeding, glaucothoe stage which is an intermediate stage which seeks appropriate habitat on the sea floor.
The red king crab, Paralithodes camtschaticus, is a very large species, sometimes reaching a carapace width of 11 in (28 cm) and a leg span of 6 ft (1.8 m). Its natural range is the Bering Sea, between the Aleutian Islands and St. Lawrence Island. It can now also be found in the Barents Sea and the European Arctic, where it was intentionally introduced and is now becoming a pest.
The blue king crab, Paralithodes platypus, lives near St. Matthew Island, the Pribilof Islands, and the Diomede Islands, Alaska, and there are populations along the coasts of Japan and Russia. Blue king crabs from the Pribilof Islands are the largest of all the king crabs, sometimes exceeding 18 lb (8 kg) in weight.
^Patsy A. McLaughlin, Tomoyuki Komai, Rafael Lemaitre & Dwi Listyo Rahayu (2010). Part I – Lithodoidea, Lomisoidea and Paguroidea (PDF). In Martyn E. Y. Low & S. H. Tan. "Annotated checklist of anomuran decapod crustaceans of the world (exclusive of the Kiwaoidea and families Chirostylidae and Galatheidae of the Galatheoidea)". Zootaxa. Suppl. 23: 5–107.
^G. C. Jensen & D. A. Armstrong (1989). "Biennial reproductive cycle of blue king crab, Paralithodes platypus, at the Pribilof Islands, Alaska and comparison to a congener Paralithodes camtschatica". Canadian Journal of Fisheries and Aquatic Sciences46 (6): 932–940. doi:10.1139/f89-120.
^A. K. Klitin & S. A. Nizyaev (1999). "The distribution and life strategies of some commercially important Far Eastern lithodid crabs in the Kuril Islands". Biologiya Morya (Vladivostok) 25 (3): 221–228.