 Naxia tumida

Naxia tumida, the little seaweed crab, dresser crab, or decorator crab, is a small crab of the family Majidae (with a carapace up to in diameter) that is common in rocky intertidal and subtidal areas on the temperate coasts of Australia, including parts of Victoria, New South Wales, Tasmania and Western Australia.It is usually found covered in seaweed that acts as camouflage, attached to the hooks on its shell.