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Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen), usually hidden entirely under the thorax. They live in all the world's oceans, in fresh water, and on land, are generally covered with a thick exoskeleton, and have a single pair of pincers. Many other animals with similar names – such as hermit crabs, king crabs, porcelain crabs, horseshoe crabs, and crab lice – are not true crabs, but many have evolved features similar to true crabs in a process of carcinisation.
A fiddler crab, sometimes known as a calling crab, may be any of more than one hundred species of semiterrestrial marine crabs in the family Ocypodidae. A smaller number of ghost crab and mangrove crab species are also found in the family Ocypodidae. This entire group is composed of small crabs, the largest being slightly over two inches (5 cm) across. Fiddler crabs are found along sea beaches and brackish intertidal mud flats, lagoons and swamps. Fiddler crabs are most well known for their sexually dimorphic claws; the males' major claw is much larger than the minor claw, while the females' claws are both the same size.
The Ocypodidae are a family of semiterrestrial crabs that includes the ghost crabs and fiddler crabs. They are found on tropical and temperate shorelines around the world.
Afrithelphusa is a genus of freshwater crabs in the family Potamonautidae. 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.
Potamonautes is a genus of African freshwater crabs in the family Potamonautidae. It is both the most widespread and most diverse genus of African freshwater crabs, including more than half the species of this continent. They are found in most freshwater habitats of the African mainland and some species are semi-terrestrial.
The Gecarcinucidae are a family of true freshwater crabs. The family Parathelphusidae is now demoted to the rank of subfamily, as the Parathelphusinae, within the Gecarcinucidae. "Family" Parathelphusidae is now considered as a junior synonym.
Pseudothelphusidae is a family of freshwater crabs found chiefly in mountain streams in the Neotropics. They are believed to have originated in the Greater Antilles and then crossed to Central America via a Pliocene land bridge.
Potamidae is a family of freshwater crabs. It includes more than 650 species and nearly 100 genera, which are placed into two subfamilies: Potaminae and Potamiscinae.
Potamonautidae is a family of freshwater crabs endemic to Africa, including the islands of Madagascar, the Seychelles, Zanzibar, Mafia, Pemba, Bioko, São Tomé, Príncipe and Sherbro Island. It comprises 18 extant genera and 138 extant species. Fossil remains dating from the Late Miocene period have been attributed to the family Potamonautidae.
Somanniathelphusa is a genus of freshwater crabs found in southeast China, Taiwan, and southeast Asia. It includes the following species:
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.
Potamon is a genus of freshwater or semiterrestrial crabs mainly found from Southern Europe through the Middle East, and as far east as north-western India. The only exception is the North African P. algeriense, which also is the only potamid of mainland Africa. Twenty species are currently recognised:. These crabs are omnivores that have a broad ecological tolerance. The adult Potaman reach up to 50 mm in size during their 10-12 year life span.
Trichodactylidae is a family of crabs, in its own superfamily, Trichodactyloidea. They are all freshwater animals from Central and South America, including some offshore islands, such as Ilhabela, São Paulo. Only one of the 50 species is known from the fossil record, Sylviocarcinus piriformis from the Miocene of Colombia. The family contains 15 genera in two subfamilies:
Johora is a genus of freshwater crabs found in the Malay Peninsula and surrounding islands. It includes the following species:
Potamocarcinus is a genus of crabs in the family Pseudothelphusidae.
Ptychophallus is a genus of crabs in the family Pseudothelphusidae.
Pseudothelphusa is a genus of crabs in the family Pseudothelphusidae, containing the following species:
Kingsleya is a genus of crabs in the family Pseudothelphusidae, containing the following species:
A number of lineages of crabs have evolved to live predominantly on land. Examples of terrestrial crabs are found in the families Gecarcinidae and Gecarcinucidae, as well as in selected genera from other families, such as Sesarma, although the term "land crab" is often used to mean solely the family Gecarcinidae.
Nanhaipotamon is a genus of freshwater crabs, in the subfamily Potamiscinae, found in southern China and Taiwan. As of 2018, 18 species have been described. The genus is named after the South China Sea, for it occurs mostly in coastal areas.
References
- ↑ Peter K. L. Ng; Danièle Guinot & Peter J. F. Davie (2008). "Systema Brachyurorum: Part I. An annotated checklist of extant Brachyuran crabs of the world" (PDF). Raffles Bulletin of Zoology . 17: 1–286. Archived from the original (PDF) on 2011-06-06.
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