The Red Rock crab is a typically-shaped crab, with five pairs of legs, the front two bearing small, blocky claws. The other legs are broad and flat, with only the tips touching the ground. The crabs round, flat shell is just over 8 centimetres (3 inches) in length.
It lives among the rocks at the often turbulent, windy shore, just above the limit of the sea spray. It feeds mainly on algae, sometimes sampling plant matter and dead animals. This crab is a quick-moving and agile crab and hard to catch, however, it is not considered very edible by humans. The Red Rock crab is used as bait by fishermen.
They mate between July and August. Like many crabs, mating occurs when the female comes into molt. The male guards her while she casts off her old carapace and waits for the new exoskeleton to harden.
Sperm is passed in packages to her abdominal flap where it remains until the eggs are fertilized. The eggs are scattered on the substrate and hatch into tiny larvae around four months later. The planktonic larvae develop through different life stages in the water column.
