Freshwater crab
common name for a non-marine crab
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.
Systematics
More than 1,300 described species of freshwater crabs are known, out of a total of 6,700 species of crabs across all environments. The total number of species of freshwater crabs, including undescribed species, is thought to be up to 65% higher, potentially up to 2,155 species, although most of the additional species are currently unknown to science. They belong to eight families, each with a limited distribution, although various crabs from other families are also able to tolerate freshwater conditions (euryhaline) or are secondarily adapted to fresh water. The phylogenetic relationships between these families is still a matter of debate, so how many times the freshwater lifestyle has evolved among the true crabs is unknown. The eight families are:
Superfamily Trichodactyloidea
Trichodactylidae (Central America and South America)
Superfamily Potamoidea
Potamidae (Mediterranean Basin and Asia)
Potamonautidae (Africa, including Madagascar)
Deckeniidae (East Africa and Seychelles) – also treated as part of Potamonautidae
Platythelphusidae (East Africa) – also treated as part of Potamonautidae
Superfamily Gecarcinucoidea
Gecarcinucidae (Asia)
Parathelphusidae (Asia and Australasia) – nowadays treated as a junior synonym of Gecarcinucidae
Superfamily Pseudothelphusoidea
Pseudothelphusidae (Central America and South America)
The fossil record of freshwater organisms is typically poor, so few fossils of freshwater crabs have been found. The oldest is Tanzanonautes tuerkayi, from the Oligocene of East Africa, and the evolution of freshwater crabs is likely to postdate the break-up of the supercontinent Gondwana.
This brief starts where responsible research should: with the source description of “Freshwater crab” as common name for a non-marine crab. Everything that follows is an evidence route, not borrowed authority.
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This entry incorporates text from “Freshwater crab” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.