Freshwater crab Freshwater crab There are around 1,300 species of freshwater crabs, 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. There are more than 1,300 described species of freshwater crabs, out of a total of 6,700 species of crabs across all environments. The total number of species of freshwater
White-edge freshwater whipray In addition, the ampullae of Lorenzini of H. signifer are intermediate in size and structure between the large, complex ampullae of its marine relatives and the small, simple ampullae of potamotrygonid stingrays, which may be a consequence of varying salinities in its environment and demands that would place on electroreception. The white-edge freshwater whipray feeds mainly on small benthic organisms, including crustaceans, molluscs, and insect larvae. Reproduction is aplacental viviparous with the developing embryos sustained by maternally produced histotroph ("uterine milk"), as is the case in other stingrays. Newborns measure across; males and females mature sexually at and across respectively.