The carapace is flattened with smooth side and rear margins, width is up to 18 mm (0.71 in),[2] and long whip-like antennae grow from the front corners, with the short rostrum extending beyond the large prominent eyes.

The large chelipeds are generally smooth with no teeth or serrations, mainly used for territorial defense among males, who usually have one enlarged.

The last pair of legs are setose, reduced in size and carried folded under a large abdominal flap, which also allows the animal to swim backwards.

Studies in New Zealand from the 1960s and 1970s showed a difference in breeding biology from north to south, with ovigerous females found all year round in Auckland, and only in the summer months around Kaikōura.

[3] In New Zealand it habits mussel beds, wharf pilings, estuaries, and the intertidal zone on rocky shores, where it is abundant beneath boulders and stones.