Freshwater crabs (Order Decapoda) belong to the same crustacean group as lobsters, prawns, crayfish, and hermit crabs, characterized by five pairs of thoracic legs (pereiopods). In freshwater crabs, the first pereiopods are modified as pincers (chelipeds), while the remaining four pairs are relatively unspecialized walking legs. The general body plan consists of a head, thorax, and abdomen, with the head and thorax covered by a broad carapace, and the abdomen reduced, flattened, and flexed under the thoracic sternum. Adult males exhibit a slim and narrow abdomen, often triangular or T-shaped, whereas females have a broad and round abdomen covering nearly the entire thoracic sternum. Adult males bear two pairs of abdominal appendages (pleopods) modified into copulatory structures known as gonopods, which are taxonomically important due to their conservative morphology.
Freshwater crabs are widely distributed in tropical and subtropical regions globally, inhabiting various aquatic and terrestrial environments. These decapods are found in diverse freshwater bodies, including mountain streams, lowland rivers, swamps, ponds, rice fields, tree holes, and leaf axils. Some species are adapted to cave environments. Primarily aquatic freshwater crabs exhibit varying degrees of tolerance to saltwater conditions, with some species being unable to survive for extended periods in saltwater.
Terrestrial species may be found away from permanent freshwater sources, utilizing forest floor litter or climbing trees. These freshwater crab species obtain water through food, dew, or capillary/osmotic uptake from moist substrata. They are primarily nocturnal, hiding during the day and foraging at night, and exhibit omnivorous scavenging behavior, feeding on plant matter and occasional live prey. Cannibalism is also observed in some species. Freshwater crabs constitute an important food resource for various fish, bird,turtle, and mammal species.