The study area and topography. A.

<p>The study area is squared in the map of China. Hypothesized zoogeographical regions (Southwest, Central, South and North regions) for Chinese freshwater crabs are separated by white dashed lines. Boundaries of the Palaearctic and Oriental realms are orange dashed lines. <b>B.</b> Topographic map of central-eastern China showing major mountain ranges, plateaus, basins and rivers. All geographical features quoted in the text are indicated.