Freshwater crab Nature (IUCN); of the species for which data are available, 32% are threatened with extinction. For instance, all but one of Sri Lanka's 50 freshwater crab species are endemic to that country, and more than half are critically endangered. 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.
Marine Biological Laboratory disease. Other marine organisms draw neuroscientists and neurobiologists to the MBL each summer, where a history of research into sensory physiology and behavior has been established. Haldan Keffer Hartline, an MBL summer investigator in the 1920s and early 1930s, uncovered several basic mechanisms of photoreceptor function through his studies on the horseshoe crab. Hartline shared the 1967 Nobel Prize with summer MBL colleague George Wald, who described the molecular basis of photoreception by showing that the light-sensitive visual pigment molecules consist of a slightly modified form of vitamin A coupled to a protein. Another long-term summer investigator, Stephen W. Kuffler,