The Japanese spider crab has the greatest leg span of any arthropod, reaching 3.8 metres (12 ft 6 in) from claw to claw. The body may grow to a size of 40 centimetres or 16 in (carapace width) and the whole crab can weigh up to 41 pounds (19 kg).  It is the males which have the longest chelipeds; females have much shorter chelipeds, which are shorter than the following pair of legs. Apart from its outstanding size, the Japanese spider crab differs from other crabs in a number of ways. The first pleopods of males are unusually twisted, and its larvae appear primitive. The crab is orange, with white spots along the legs. It is reported to have a gentle disposition “in spite of its ferocious appearance”.

The Japanese spider crab has the greatest leg span of any arthropod, reaching 3.8 metres (12 ft 6 in) from claw to claw. The body may grow to a size of 40 centimetres or 16 in (carapace width) and the whole crab can weigh up to 41 pounds (19 kg).  It is the males which have the longest chelipeds; females have much shorter chelipeds, which are shorter than the following pair of legs. Apart from its outstanding size, the Japanese spider crab differs from other crabs in a number of ways. The first pleopods of males are unusually twisted, and its larvae appear primitive. The crab is orange, with white spots along the legs. It is reported to have a gentle disposition “in spite of its ferocious appearance”.