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Geothelphusa

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Geothelphusa
Geothelphusa dehaani, the sawagani crab
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Class: Malacostraca
Order: Decapoda
Suborder: Pleocyemata
Infraorder: Brachyura
Family: Potamidae
Subfamily: Potamiscinae
Genus: Geothelphusa
Stimpson, 1858
Type species
Geothelphusa obtusipes
Stimpson, 1858
Synonyms

Geothelphusa is a genus of freshwater crabs within the family Potamidae, native to East Asia, with a distribution spanning Japan, Taiwan, China, and Korea. Established by William Stimpson in 1858, it ranks among the most diverse genera in Potamidae, encompassing over 50 recognized species.

Taxonomy

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Geothelphusa was established by William Stimpson in 1858, designating Geothelphusa obtusipes as the type species.[1] It is classified under the family Potamidae, subfamily Potamiscinae, within the superfamily Potamoidea.[2] The genus has a complex taxonomic history due to morphological similarities among species, resulting in frequent synonymy and reclassification.[3] A 2011 study by Shih et al. demonstrated that speciation within Geothelphusa was influenced by Pleistocene climatic shifts, with two primary clades diverging approximately 5.3 million years ago.[3] Recent research by Shih et al. (2024) refined the taxonomy by redescribing Geothelphusa dehaani and identifying two new species from Japan, underscoring ongoing taxonomic advancements.[4]

Description

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Geothelphusa species are small to medium-sized freshwater crabs, with carapace widths ranging from 20 to 50 mm.[5] The carapace is typically smooth and convex, exhibiting a trapezoidal shape with a distinct cervical groove. The frontal margin is straight or slightly concave, and the anterolateral margins are arched and cristate.[6] Their legs are long and slender, adapted for both aquatic and terrestrial locomotion, while their robust claws serve for feeding and defense.[7] Coloration varies across species, from reddish-brown to blue or green, often reflecting regional differences.[5]

Geothelphusa dehaani, the sawagani crab, features a reddish-brown carapace, reddish legs, and milky white claws, with regional variants displaying paler brown or blue hues.[5]

Distribution

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Geothelphusa is distributed across East Asia, including Japan, Taiwan, China, and Korea.[2][3] The genus exhibits remarkable diversity in Taiwan, where over 40 species have been documented, many of which are endemic.[6] In Japan, species occur throughout the main islands, with G. dehaani being the most widespread and recognized.[4] Additional populations are recorded in the Ryukyu Islands and other offshore regions.

Ecology

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Geothelphusa crabs inhabit clear mountain streams, rivers, and swamps, frequently sheltering beneath rocks or within leaf litter.[5] They are omnivorous, consuming insects, snails, earthworms, plant matter, and detritus, functioning as both predators and scavengers. Primarily nocturnal, they forage at night and remain concealed during the day, with activity peaking on rainy or humid days.[5]

Reproduction takes place in summer, with females carrying around 50 eggs on their abdomens until hatching. The genus displays direct development, bypassing a planktonic larval stage, which restricts dispersal and fosters localized populations.[4] Their lifespan is estimated at 10 years, during which they exhibit hibernation-like behavior in winter.[5][3] Some species, such as G. dehaani, migrate upstream during breeding and may display territorial tendencies.[4] Sensitive to water quality, these crabs are often used as bioindicators of environmental health. In Japan, sawagani have also appeared in local cuisine and popular media, reflecting their cultural significance.[8]

Species

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The World Register of Marine Species recognizes the following species:[2]

Synonyms

References

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  1. ^ Stimpson, William (1858). "Prodromus descriptionis animalium evertebratorum, quae in Expeditione ad Oceanum Pacificum Septentrionalem, a Republica Federata missa, Cadwaladaro Ringgold et Johanne Rodgers Ducibus, observavit et descripsit. Pars V. Crustacea Ocypodoidea". Proceedings of the Academy of Natural Sciences of Philadelphia. 10: 93–110.
  2. ^ a b c De Grave, Sammy (2019). "Geothelphusa Stimpson, 1858". World Register of Marine Species. Retrieved 2025-05-19.
  3. ^ a b c d Shih, H. T.; Ng, P. K. L.; Naruse, T.; Shokita, S.; Liu, M. Y. (2011). "Phylogenetic relationships among freshwater crab species of Geothelphusa from northern Taiwan and the Yaeyama Group of islands". Zoologischer Anzeiger. 250 (4): 457–471. doi:10.1016/j.jcz.2011.07.004.
  4. ^ a b c d Shih, Hsi-Te; Naruse, Tohru; Yeo, Darren C. J. (2024). "The identity of the Japanese freshwater crab Geothelphusa dehaani (White, 1847) (Decapoda: Brachyura: Potamidae), with descriptions of two new species from Japan". Journal of Crustacean Biology. 44 (2): ruad027. doi:10.1093/jcbiol/ruad027.
  5. ^ a b c d e f "Japanese Freshwater Crab". Orbis Pictus. Retrieved 2025-05-19.
  6. ^ a b Shy, Jhy-Yun; Ng, Peter K. L.; Yu, H. P. (1994). "Crabs of the genus Geothelphusa Stimpson, 1858, of Taiwan (Crustacea: Decapoda: Brachyura: Potamidae)". Raffles Bulletin of Zoology. 42 (4): 781–846.
  7. ^ "Sawagani Crab". Takao 599 Museum. Retrieved 2025-05-19.
  8. ^ Schreiber, Mark (2002). "In a pinch, these will do just fine". The Japan Times. Retrieved 2025-05-19.
  9. ^ a b Shy, Jhy-Yun; Shih, Hsi-Te; Mao, Jean-Jay (2021). "Geothelphusa boreas, A New Montane Freshwater Crab (Crustacea: Potamidae: Geothelphusa) from northeastern Taiwan, and the Identity of G. hirsuta Tan & Liu, 1998". Zootaxa. 5060 (1): 93–104. doi:10.11646/zootaxa.5060.1.4.
  10. ^ Shy, Jhy-Yun; Shih, Hsi-Te; Mao, Jean-Jay (2014). "Description of A New Montane Freshwater Crab (Crustacea: Potamidae: Geothelphusa) from northern Taiwan". Zootaxa. 3869 (5): 565–572. doi:10.11646/zootaxa.3869.5.6.
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Media related to Geothelphusa at Wikimedia Commons Data related to Geothelphusa at Wikispecies

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