These crabs cut a chosen sponge or sea squirt to fit themselves, then hold it on their head with specialized hind legs, according to Andrew Hosie, who holds a Ph.D. in aquatic zoology and is the curator of crustacea and worms at the Western Australian Museum.
As amazing as this is, Lamarckdromia beagle isn’t the only crab that dons a hat. You can see an example of another crab species using a similar tactic below. (However, you could argue that Lamarckdromia beagle wears it better.)