In Chinese, these are known as 花蟹 (huā xiè), literally 'flower crabs'. Bright blue when raw. I buy them live.
Stir fried with lots of chopped garlic, grated ginger, chopped green chilli,. Added Vietnamese fish sauce and Chinese oyster sauce. Finished with chopped chives and coriander leaf.
With rice to mop up sauce. Skipped vegetation tonight.
Messy finger food - there is no dignified way to eat these.
Followed by more fresh lychees than is probably safe.