Leptomithrax gaimardii (common name - Great spider-crab) is a species of crab in the Majidae family, first described by Henri Milne-Edwards in 1834 as Paramithrax gaimardii,[3][4] from a specimen (erroneously said to be) found in New Zealand waters[3] by Joseph Paul Gaimard who is honoured by the species epithet.

[4] It is found in coastal waters of Western Australia, South Australia, Victoria, New South Wales, and Tasmania.

[1] When breeding these crabs form groups of often greater than 100 crabs, Breeding occurs just before winter moulting when they are vulnerable to predation because of their soft shells.

The large congregations make them less vulnerable.

[1] The crab is a scavenger, and is found in seaweed, reef and sand areas at depths of up to 820 m (2,690 ft).