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More than 1,300 described species of freshwater crabs are known, out of a total of 6,700 species of crabs across all environments. [1] 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. [1]
As with other crabs, the body is roughly square, with the reduced abdomen tucked beneath the thorax. The thorax bears five pairs of legs, the first of which is armed with large claws. The life span of P. fluviatile is typically 10–12 years. [7] Moulting does not occur in winter. [8]
The fiddler crabs' carapaces are broadened at the front, while the carapaces of ghost crabs are more or less box-like. Lastly, the eyes of ghost crabs have large and elongated eyestalks, with the corneas occupying the entire lower part, while in fiddler crabs the eyestalks are long and thin, with the corneas small and located at the tip. [3] [4]
Snow crabs, a cold-water Arctic species, thrive overwhelmingly in areas where water temperatures are below 2 degrees Celsius, though they can physically function in waters up to 12 degrees Celsius.
The fiddler crabs sold in pet stores generally come from brackish water lagoons. Because they live in lower salinity water, pet stores may call them fresh-water crabs, but they cannot survive indefinitely in fresh water. [37] Fiddler crabs have been known to attack small fish in captivity, as opposed to their natural feeding habits. [38]
In the winter, a female crab will bury herself in the sand and become inactive in order to protect her eggs. [3] Eggs typically hatch in the spring, although exact time varies with location. [3] [9] Young crabs are free-swimming after hatching and are diel vertical migrators that can be found at depths up to 80 ft (24 m) during the day. [9]
The desire for, or occurrence of, more sleep during winter may have to do with how light fluctuates throughout the year, or with the behavioral and mental health changes that can result.
The carapace of G. ruricola grows in width at a rate of about 1 in (25 mm) per year, with the crabs reaching maturity after 5 years, and living for up to 10 years in total. [6] G. ruricola crabs have a number of adaptations to terrestrial life, mostly regarding water conservation. They are nocturnal, to prevent the hot sun from drying them out.