New Zealand has a considerable fauna of crabs, but, except for a deep-water southern species, they are not large enough to be of commercial value. The large shore crab (Leptograpsus variegatus) is the aggressive creature that scuttles away into rock crevices when disturbed. With back to the wall he always shows fight – claws open and raised ready to contest with any intruder. This crab grows to about 6 in. across and is mottled dull reddish-purple and white edged with violet. The swimming crab (Ovalipes bipustulatus) is common at low tide on open sandy beaches. Note that the hindermost pair of legs are designed as paddles, equally effective both for swimming and for quick burrowing into the sand. When disturbed this crab just disappears vertically into the sand with great rapidity. The camouflaged spider crab (Paramithrax peronii) is the slender-legged triangular-bodied crab which is rendered inconspicuous by a tangled covering of marine growth, self-attached to hooked, hairlike processes adapted for the purpose. One small freshwater crab is known from northern New Zealand (Hymenosoma lacustris), related to species from Norfolk Island, Lord Howe Island, and Victoria. The half crab (Petrolisthes elongatus) one of our most abundant species, literally swarms under intertidal stones in the north. It differs from other crabs in possessing long antennae; its colouring is greenish-blue.
by Arthur William Baden Powell, Assistant Director, Auckland Institute and Museum.