The Largest Arthropod in the World: The Japanese spider crab

The Japanese spider crab 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). In its natural habitat, the Japanese spider crab feeds on shellfish and animal carcasses and may live for up to 100 years. [Source]