The Giant Spider Crab from Japan. Macrocheira kaempferi, is a species of marine crab that lives in the waters around Japan. It has the largest leg span of any arthropod, reaching up to 3.8 metres (12 ft) and weighing up to 41 pounds (19 kg). It is the subject of small-scale fishery which has led to a few conservation measures. Read more at http://en.wikipedia.org/wiki/Japanese_spider_crab