Japanese Mitten Crab or Mokuzugani i Japanese is also called Mokuzou, Zugani, Tsugani or Kegani.
It caught alsmost everywhere in Japan in Autumn and Winter.
In Autumn the females come to lay their eggs at river mouths.
Plenty are found along the Izu Peninsula in Shizuoka Prefecture.
They are caught in boxes baited with fish.
As for food, they can be eaten boiled in soups or crushed with their shell and cooked with miso. They could even be prepared as French bisque.
The female specimens are particularly appreciated for their egg sacs.
These boiled egg sacs with the meat make for delicious sushi nigiri or gunkan!
SHIZUOKA SUSHI & SASHIMI: The other Jewels of Japan 
Hi Robert, this seems to be the same species as the mitten crabs residing in the Thames River in England and the Shanghai crabs too. Too similar to not be the same i feel. What do you make of this? π
Could evry well be, although the distances involved would suggest they are all different subspecies!
There are two different species, Eriocheir japonica is native to Japan. The Shanghai hairy crab is Eriocheir sinensis, this is the one that is an invasive species in Britain. They grow a bit larger than their Japanese cousins. Both are edible!
Cheers, Daniel!