King Crab

King crabs are decapod crustaceans in the family Lithodidae that are chiefly found in cold seas. Because of their large size and the taste of their meat, many species are widely caught and sold as food with the most common being the red king crab (Paralithodes camtschaticus).

King crabs Temporal range: Miocene–Recent PreꞒ Ꞓ O S D C P T J K Pg N
Paralithodes californiensis
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Malacostraca
Order:	Decapoda
Suborder:	Pleocyemata
(unranked):	Reptantia
Infraorder:	Anomura
Superfamily:	Paguroidea Samouelle, 1819
Family:	Lithodidae Samouelle, 1819
Genera
Hapalogastrinae Acantholithodes Dermaturus Hapalogaster Oedignathus Placetron Lithodinae Cryptolithodes Glyptolithodes Lithodes Lopholithodes Neolithodes Paralithodes Paralomis Phyllolithodes Rhinolithodes Sculptolithodes

King crabs are not true crabs, and are generally thought to be derived from hermit crab ancestors within the Paguridae, which may explain the asymmetry still found in the adult forms. This ancestry is supported by several anatomical peculiarities which are present only in king crabs and hermit crabs. Although some doubt still exists about this hypothesis, 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 spiral shell.

In 2007, the king crabs were moved from their classification among the hermit crabs in the superfamily Paguroidea into a separate superfamily, Lithodoidea. This was not without controversy, as there is widespread consensus in the scientific community that king crabs are derived from hermit crabs and closely related to pagurid hermit crabs; therefore, a separate superfamily in the classification poorly reflected the phylogenetic relationship of this taxon. In 2023, king crabs were folded back into Paguroidea, with Lithodoidea being considered superseded.

As of April 2024^[update], 137 species of king crab (one extinct) are known in 15 genera. These are split across its two subfamilies – Hapalogastrinae and Lithodinae – and include:

Hapalogastrinae

Lithodinae

Glyptolithodes

Glyptolithodes is found chiefly in the Southern Hemisphere, but extending as far north as California, although all its closest relatives live in the Northern Hemisphere. Its single species, G. cristatipes, was originally placed in the genus Rhinolithodes.

Paralithodes

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 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 intermediate glaucothoe stage which seeks appropriate habitat on the sea floor.

 

Paralithodes camtschaticus

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 around the Kamchatka Peninsula area, between the Aleutian Islands and St. Lawrence Island. It can also be found in the Barents Sea and the European Arctic, where it was intentionally introduced and has now become a pest. By 2022 they had spread to the North Sea, becoming both a lucrative new stock to British fisheries, and an invasive species.

Paralithodes platypus

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.

Juveniles of species of king crabs, including Neolithodes diomedeae, use a species (Scotoplanes Sp. A) of sea cucumber (often known as “sea pigs”) as hosts and can be found on top of and under Scotoplanes. The Scotoplanes reduce the risk of predation for the N. diomedeae, while the Scotoplanes are not harmed from being hosts, which supports the consensus that the two organisms have a commensal relationship.

Some species of king crab, including those of the genera Lithodes, Neolithodes, Paralithodes, and likely Echidnocerus, act as hosts to some parasitic species of careproctus fish. The careproctus lays eggs in the gill chamber of the king crab which serves as a well-protected and aerated area for the eggs to reside until they hatch. On occasion king crabs have been found to be host to the eggs of multiple species of careproctus simultaneously.^{[citation needed]}

• Alaskan king crab fishing