Sweet Water Crab...
Found a blue crab walking home with my daughter from the bus stop. In the middle of town, Lafayette LA.
They live in some of the deeper suburban ditches here, in front of the homes. Along with ditch crawdads and various frog/toad species, see the tadpoles.
I found this crab under the rocks at the Pacific Coast of California. It seems that for a instance his original color is purple but when I saw it closer it has his green color too. But his tongs are purple as well as his abdomen.
Callinectes sapidus, the Atlantic blue crab; Volusia county, Florida; 17 March 2015. http://phostracks.com.
may be イワガニ.
The decapods or Decapoda (literally "ten-footed") are an order of crustaceans within the class Malacostraca, including many familiar groups, such as crayfish, crabs, lobsters, prawns and shrimp. Most decapods are scavengers. The order is estimated to contain nearly 15,000 species in around 2,700 genera, with approximately 3,300 fossil species. Nearly half of these species are crabs, with the shrimp (c. 3000 species) and Anomura (including hermit crabs, porcelain crabs, squat lobsters: (c. 2500 species), making up the bulk...