* Japanese name: Sawagani
* Scientific name: Geothelphusa dehaani
* Description: Crabs are decapods, which means "10 legs." Marsh crabs are usually red-and-cream colored, but may be found in other colors -- perhaps caused by mutations -- in different parts of the country. Crabs have exoskeletons like insects, but even tougher ones. Their front two legs are equipped with strong pincers, used for eating and fighting. Marsh crabs are quite small, with shells 2 cm wide.
* Where to find them: The marsh crab is a freshwater crab, so it can be found in most parts of Japan, from Hokkaido to Kyushu, wherever there is a river, stream or marsh. They can also be found in urban areas, sometimes hiding in the cracks in stone walls. When it rains, they can be seen strolling about on rocks and walls.
* Food: Marsh crabs are omnivores, eating both plants and animals. They are important members of the detritus food chain. Detritus is the name given to the broken pieces of dead plants and animals that fall to the bottom of rivers. If this debris was left uneaten, it would pile up. When the crabs die, they are often eaten by river snails. Black bears also like to eat them.
* Special features: Most crabs lay hundreds of tiny eggs into the water, but female marsh crabs retain their eggs within their body. Their eggs are 3-4 mm in diameter, much larger than in most other crabs of the same size. The young develop through all the larval stages inside the egg, safe inside the abdomen of the female. Tiny, fully formed crabs then hatch directly from inside the female and are released into the water.