Purple Rock Crab

''Hemigrapsus sexdentatus'', known as the common shore crab, is a large-eyed marine crab of the family Grapsidae, endemic to the coasts of New Zealand. However, it is not found in the Chatham Islands or the southern islands. It can grow to around 40 millimetres shell width.

Rock crabs are known to feed on sea snails by crushing their shells through the use of a chela . Paul Bourdeau, of the Stony Brook University, calls them, "the meanest organisms that I have ever come across".