The Christmas Island red crab is a species of land crab that is endemic to Christmas Island and Cocos (Keeling) Islands in the Indian Ocean. Although restricted to a relatively small area, an estimated 43.7 million adult red crabs once lived on Christmas Island alone, but the accidental introduction of the yellow crazy ant is believed to have killed about 10–15 million of these in recent years. Christmas Island red crabs make an annual mass migration to the sea to lay their eggs in the ocean. Although its population is under great assault by the ants, as of 2020 the red crab had not been assessed by the International Union for Conservation of Nature (IUCN) and it was not listed on their Red List. The crab's annual mass migration to the sea for spawning is described as an "epic" event. Millions emerge at the same time, halting road traffic and covering the ground in a thick carpet of crabs.
Afrithelphusa is a genus of freshwater crabs in the family Deckeniidae. It contains four species, all of which were formerly listed as critically endangered by the International Union for Conservation of Nature (IUCN). They are all endemic to the Upper Guinean forests of Guinea and Sierra Leone.
Ceylonthelphusa is a genus of freshwater crabs endemic to Sri Lanka, where they live in moist lowland forests, swamps and rivers. Many of the species are on the IUCN Red List of threatened species, with the greatest risk factor being habitat loss. Ceylonthelphusa contains these species:
Oziotelphusa is a genus of freshwater crabs in the family Gecarcinucidae. Its members are found in Sri Lanka and southern India. The genus was formerly placed within family Parathelphusidae, but now it is accepted that Parathelphusidae is the junior synonym of Gecarcinucidae.
Perbrinckia is a genus of freshwater crabs of the family Gecarcinucidae that is endemic to Sri Lanka, named after Per Brinck. Its natural habitats are subtropical or tropical moist lowland forests, subtropical or tropical swamps, and rivers. It contains 14 species, most of which are included on the IUCN Red List as critically endangered species (CR) or vulnerable species (VU) because they are threatened by habitat loss; only one species is of least concern (LC).
Spiralothelphusa is a genus of freshwater crabs in the family Gecarcinucidae. It contains these species, all of which are included on the IUCN Red List:
Lybia is a genus of small crabs in the family Xanthidae. Their common names include boxer crabs, boxing crabs and pom-pom crabs. They are notable for their mutualism with sea anemones, which they hold in their claws for defense. In return, the anemones get carried around, which may enable them to capture more food particles with their tentacles. Boxer crabs use at least three species of anemones, including Bundeopsis spp. and Triactis producta. The bonding with the anemone is not needed for survival, however, and boxer crabs have frequently been known to live without them, sometimes substituting other organisms such as sponges and corals for the sea anemones.
Tiwaripotamon vietnamicum is a species of crab. Originally described as a species of Geothelphusa, it is now treated as part of the genus Tiwaripotamon, although it has also been suggested as a member of Hainanpotamon. It is only known from a single locality in Cúc Phương National Park, Ninh Bình Province, Vietnam.
The coconut crab is a terrestrial species of giant hermit crab, and is also known as the robber crab or palm thief. It is the largest terrestrial arthropod known, with a weight of up to 4.1 kg (9 lb). The distance from the tip of one leg to the tip of another can be as wide as 1 m. It is found on islands across the Indian and Pacific Oceans, as far east as the Gambier Islands, Pitcairn Islands and Caroline Island and as far west as Zanzibar. While its range broadly shadows the distribution of the coconut palm, the coconut crab has been extirpated from most areas with a significant human population such as mainland Australia and Madagascar.
Potamon fluviatile is a freshwater crab found in or near wooded streams, rivers and lakes in Southern Europe. It is an omnivore with broad ecological tolerances, and adults typically reach 50 mm (2 in) in size during their 10–12 year lifespan. They inhabit burrows and are aggressive, apparently outcompeting native crayfish.
Deckenia is a genus of freshwater crabs from East Africa, in the family Potamonautidae, or sometimes in a family of its own, Deckeniidae. The genus was named by Hilgendorf after Karl Klaus von der Decken who collected the first examples during his expeditions to Africa. Both species live in swamps from Eyl in Somalia to Dar es Salaam, Tanzania, both in coastal areas and further inland. A third species, Deckenia alluaudi, lives in the Seychelles, and has been transferred to a separate genus, Seychellum.
Johora singaporensis, the Singapore stream crab or Singapore freshwater crab, is a critically endangered species of freshwater crab endemic to Singapore. It grows to a size of 30 millimetres (1.2 in) wide.
Disparithelphusa pecki is a species of freshwater crab in the family Pseudothelphusidae, and the only species in the genus Disparithelphusa.
Brasiliothelphusa tapajoensis is a species of freshwater crabs in the family Pseudothelphusidae, and the only species in the genus Brasiliothelphusa. It was described in 1986 from specimens caught in the Rio Tapajós in the state of Pará, Brazil. It is listed as Data Deficient on the IUCN Red List.
Achlidon agrestis is a species of crab in the family Pseudothelphusidae, and the only species in the genus Achlidon. It lives in rivers in Mexico and Costa Rica.
Eidocamptophallus chacei is a species of crab in the family Pseudothelphusidae, and the only species in the genus Eidocamptophallus.
Prionothelphusa is a genus of freshwater crabs in the family Pseudothelphusidae, containing the single species Prionothelphusa eliasi. It lives in Colombia, Venezuela and Brazil in the drainages of the Rio Negro river draining the Guyana Shield, and is listed as Least Concern on the IUCN Red List.
Potamon ibericum is a Eurasian species of freshwater crab. It is an omnivore that feeds on land, but returns regularly to the water, and can survive short periods of drought in burrows and under stones. Its natural range stretches from north-eastern Greece, around both sides of the Black Sea and to beyond the Caspian Sea; populations have also been introduced to southern France. It is included as a near threatened species on the IUCN Red List, and is included in the Red Data Book for Ukraine.
Around 1,300 species of freshwater crabs are distributed throughout the tropics and subtropics, divided among eight families. They show direct development and maternal care of a small number of offspring, in contrast to marine crabs, which release thousands of planktonic larvae. This limits the dispersal abilities of freshwater crabs, so they tend to be endemic to small areas. As a result, a large proportion are threatened with extinction.
Seychellum alluaudi is a species of freshwater crab endemic to the Seychelles, and the only true freshwater crab in that country. It lives in rainforest streams on the archipelago's granitic high islands. Although it may be abundant, little is known about its biology. If its habitat were to decline in quality, S. alluaudi might become endangered, but it is currently listed as Vulnerable on the IUCN Red List.
