Whilst the name of this species indicates a mottled purple crab the reality is that this species does vary greatly with colours from that mottled purple to dark reds and oranges. The key to identifying this species lays in the shape of the carapace the lack of the notches behind the eyes and being more rounded or curved along the sides of the carapace and lacks the tufts of hairs at the base of the legs.
They can survive out of the water for several hours. As scavengers this species feeds on decaying seaweeds and other sea life along the shorelines and are often found under rocks at low tide scurrying for cover when disturbed.
Images showing the key charateristics of this species to help with identification
Under rocks at mid to high intertidal levels
Grows up to around 4cm