King crabs orstone crabs are marinedecapodcrustaceans of thefamilyLithodidae[b] that are found chiefly in deep waters and are adapted to cold environments.[3][4] They are composed of two subfamilies:Lithodinae, which tend to inhabit deep waters, are globally distributed, and comprise the majority of the family's species diversity;[4][5] andHapalogastrinae, which are endemic to the North Pacific and inhabit exclusively shallow waters.[4] King crabs superficially resembletrue crabs but are generally understood to be closest to thepagurid hermit crabs.[6][5] This placement of king crabs among the hermit crabs is supported by several anatomical peculiarities which are present only in king crabs and hermit crabs, making them a prominent example ofcarcinisation among decapods.[7] Several species of king crabs, especially inAlaskan and southernSouth American waters, are targeted bycommercial fisheries and have been subject tooverfishing.[3][8][9]
King crabs are believed to have originated during theEarly Miocene in shallow North Pacific waters, where most genera – including all Hapalogastrinae – are distributed and where they exhibit a high amount ofmorphological diversity.[5][10] Since the late 1800s, carcinologists have suspected that king crabs are hermit crabs who underwent secondary calcification and left theirshell.[5]
The king crab family Lithodidae was created and placed among thetrue crabs in 1819 by zoologistGeorge Samouelle to hold the then-recently-described genusLithodes.[1] In 2007, examining themonophyly of the decapod infraorderAnomura, carcinologistPatsy McLaughlin and colleagues moved the king crabs from their classification within the hermit crabsuperfamilyPaguroidea into a separate superfamily, Lithodoidea.[11][2] They furthermore found Lithodoidea to be a sister clade to the mole crab superfamilyHippoidea.[11] This was controversial, as there is strongphylogenetic evidence that king crabs are derived from hermit crabs and closely related topagurid hermit crabs.[7][12][13] In 2023, king crabs were folded back into Paguroidea, with Lithodoidea being considered superseded.[6] The king crabs' relationship to other hermit crabs, as well as the family's internal phylogeny, can be seen in the following twocladograms:[5][14]
King crabs often feature prominent spines, which shrink as they mature.[18] Pictured is a juvenile and adult specimen ofLithodes aotearoa.
King crabs are a morphologically diverse group, distinctive amonghermit crabs for their superficial similarity totrue crabs.[5][19]
They have five pairs of legs, called pereopods:[c] the first – frontmost – set arechelipeds whose right side is often larger and more robust than the left; the second, third, and fourth are walking legs tipped with sharpdactyli; and the fifth, used for cleaning, are very small and generally sit inside the branchial chamber.[21] Starting from the carapace, the walking legs can be divided into acoxa, ischiobasis, merus, carpus, propodus, and finally dactylus; the chelipeds lack coxae and are instead composed of an ischiobasis, merus, carpus, and palm which then forks into a movable dactylus and an inflexible pollex.[22]
On their underside, they have a shortabdomen – composed of plates or nodules – which is asymmetrical in females.[21] This abdomen (sometimes called a pleon)[5] is folded against the underside of thecephalothorax and is composed of six segments – calledsomites or pleonites – and atelson.[23][24][d] In Hapalogastrinae, this abdomen is soft, while it is hard and calcified in members of Lithodinae.[5] Lithodids lack any sort ofuropod seen in somedecapods.[21]
King crabs are typically found in deep waters, especially inpolar and subpolar regions and nearhydrothermal vents andcold seeps.[3] Members of Lithodinae can be found in all five of the world's oceans, namely thePacific,[26]Atlantic,[26]Indian,[27]Southern,[28] andArctic,[29] while members of Hapalogastrinae are only found in the North Pacific.[4] Members of Hapalogastrinae exhibit a tolerance for higher temperatures than Lithodinae; whereas Lithodinae tend to live exclusively in deep waters or – less commonly – high-latitude shallow waters, Hapalogastrinae are found only in shallow waters (<100 m (330 ft)).[4] At the deepest, members of the Lithodinae generaParalomis,Neolithodes, andLithodes have been found at depths of 4,152 m (13,622 ft), 3,207 m (10,522 ft), and 1,821 m (5,974 ft), respectively.[30]
Because of their large size, the taste of their meat, and their status as adelicacy, some species of king crabs are caught and sold as food.[31][9][8] Red (Paralithodes camtschaticus) and blue (Paralithodes platypus) king crabs are heavily targeted bycommercial fisheries inAlaska and have been for several decades. However, populations have fluctuated in the past 25 years, and some areas are currently closed due tooverfishing.[32][33][34][35] Alaskan fisheries additionally target the golden king crab (Lithodes aequispinus).[36] In South America, both the southern king crab (Lithodes santolla) and several species ofParalomis are targeted by commercial fisheries,[31][3] and as a result, the population ofL. santolla has seen a dramatic decline.[9]
Juveniles of species of king crabs, includingNeolithodes diomedeae, use a species (Scotoplanes Sp. A) ofsea cucumber (often known as "sea pigs") ashosts and can be found on top of and underScotoplanes. TheScotoplanes reduce the risk of predation for theN. diomedeae, while theScotoplanes are not harmed from being hosts, which supports the consensus that the two organisms have acommensal relationship.[37] Endosymbiotic microorganisms of the order Eccrinida have been found inParalithodes camtschaticus andLithodes maja, living in theirhindgut between molts.[38]
Some species of king crab, including those of the generaLithodes,Neolithodes,Paralithodes, and likelyEchidnocerus, act ashosts to someparasitic species ofcareproctus fish.[39] 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.[39] On occasion king crabs have been found to be host to the eggs of multiple species of careproctus simultaneously.[39] King crabs are additionally parasitized byrhizocephalan genusBriarosaccus, a type of barnacle.[40] The barnacle irreversibly sterilizes the crab, and over 50% of some king crab populations are affected.[40]
^abDvoretsky, Alexander G.; Dvoretsky, Vladimir G. (November 2017). "Red king crab (Paralithodes camtschaticus) fisheries in Russian waters: historical review and present status".Reviews in Fish Biology and Fisheries.28 (2):331–353.doi:10.1007/s11160-017-9510-1.ISSN0960-3166.
^Klitin, A.K.; Nizyaev, S.A. (1999). "The distribution and life strategies of some commercially important Far Eastern lithodid crabs in the Kuril Islands".Biologiya Morya.25 (3). Vladivostok:221–228.ISSN1063-0740.
^Barry, James P.; Taylor, Josi R.; Kuhnz, Linda A.; DeVogelaere, Andrew P. (2016-10-15). "Symbiosis between the holothurianScotoplanes sp. A and the lithodid crabNeolithodes diomedeae on a featureless bathyal sediment plain".Marine Ecology.38 (2) e12396.doi:10.1111/maec.12396.eISSN1439-0485.
^Pavlova, L.V. (2018). "First Finding of Representatives of the Eccrinida Order in the Digestive Tract of King Crab Specie from the Barents Sea".Doklady Biological Sciences.483 (1):231–234.doi:10.1134/S0012496618060066.ISSN0012-4966.PMID30603945.
Poore, Gary C. B.;Ahyong, Shane T. (2023). "Anomura".Marine Decapod Crustacea: A Guide to Families and Genera of the World. CRC Press. pp. 311–317.ISBN978-1-4863-1178-1.
The dictionary definition ofking crab at Wiktionary
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