Freshwater crab

Source: Wikipedia, the free encyclopedia.
Potamon ibericum (Potamidae) in Georgia
Parathelphusidae
) in Indonesia

Around 1,300 species of freshwater crabs are distributed throughout the

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

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.[1] 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.[1] 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.[1]
The eight families are:

Superfamily
Trichodactyloidea
Superfamily Potamoidea
Superfamily Gecarcinucoidea
Superfamily Pseudothelphusoidea

The

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.[2]

Members of the family

Brachyura).[3]

Description and lifecycle

Seven round translucent spheres: inside some of them, a pair of compound eyes can be seen.
Eggs of Potamon fluviatile containing fully formed juvenile crabs

The

larval stages passing within the egg.[1] The broods comprise only a few hundred eggs (compared to hundreds of thousands for marine crabs), each of which is quite large, at a diameter around 1 mm (0.04 in).[4]

The colonisation of fresh water has required crabs to alter their water balance; freshwater crabs can reabsorb salt from their

preadapted freshwater crabs for terrestrial living, although freshwater crabs need to return to water periodically to excrete ammonia.[4]

Ecology and conservation

Freshwater crabs are found throughout the tropical and subtropical regions of the world.

secondary hosts of flukes in the genus Paragonimus, which causes paragonimiasis in humans.[4]

The majority of species are narrow endemics, occurring in only a small geographical area. This is at least partly attributable to their poor dispersal abilities and low fecundity,[1] and to habitat fragmentation caused by the world's human population.[5] In West Africa, species that live in savannas have wider ranges than species from the rainforest; in East Africa, species from the mountains have restricted distributions, while lowland species are more widespread.[4]

Every species of freshwater crab described so far has been assessed by the

critically endangered.[5]

References

  1. ^
    ISBN 978-1-4020-8258-0. {{cite book}}: |journal= ignored (help
    )
  2. doi:10.1016/j.jcz.2011.07.001
    .
  3. JSTOR 1548413
    .
  4. ^
    PDF). Freshwater Forum
    . 21: 3–26.
  5. ^
    ISBN 978-2-8317-1063-1
    .
  6. ISBN 978-2-8317-1063-1
    .

External links
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