Flower crabs with red ties.

Portunus pelagicus, also known as the flower crab, blue crab, blue swimmer crab, blue manna crab or sand crab, is a large crab found in the intertidal estuaries of the Indian and Pacific Oceans (Asian coasts) and the Middle-Eastern coast of the Mediterranean Sea. The name "flower crab" is used in east Asian countries while the latter names are used in Australia. The crabs are widely distributed in eastern Africa, Southeast Asia, East Asia, Australia and New Zealand (source: Wikipedia article).

They are part of the Portunidae, a family of crabs which contains the swimming crabs, characterised by the flattening of the fifth pair of legs into broad paddles, which are used for swimming.

Photo taken at the fish market in Kota Kinabalu (Borneo)