The Japanese spider crab (高脚蟹 takāshigani, lit. “tall-footed crab”), 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).

During the larval stage the young crab looks nothing like its parents. It is small and transparent with a round, legless body and usually drifts as plankton at the surface of the ocean.

Nightmare fuel time.

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Quoted text via Wikipedia.