Flat Rock Crab (Percnon planissimum) トゲアシガニ – size 2.5cm
The Flat Rock Crab lives in the rocks. It is often in the shallow surge zone but can go deeper and out of the water too. Enoshima 2011
A Flat Rock Crab in Hawaii. These were deeper than the ones I saw in Japan maybe about 6m. Kauai 2020