[5] The carapace is tear-shaped with a wide, rounded posterior which tapers to a point at its snout, or rostrum.

Young crabs deliberately attach algae, bryozoans, hydroids, sponges, and other creatures to their exoskeletons as a form of camouflage to hide from predators.

This species stops molting when it reaches sexual maturity, however, and a layer of algae often develops on the long-lived adult exoskeleton, giving these crabs a green appearance.

Sheep crabs are quite mobile, achieving speeds of 0.4 kilometres per hour (0.25 mph),[2] foraging on soft and rocky bottoms, as well as pilings.

The aggregations which have been studied in detail are composed only of adults and included females and at least one male.

Sheep crabs are typically solitary, and it has been hypothesized that the purpose of the aggregations is to increase the concentration of a chemical signal, a pheromone, from the females to attract males for mating.

[2] A male crab grasps a female for mating and delivers a sperm packet.

Orange eggs are the freshest, red are of intermediate development, and brown can be seen to have eyes and are ready to be released.

Brooding females have been found year-round suggesting that there is no strong seasonal peak in reproduction.

[2] The sheep crab has a rigid and thick exoskeleton which presents an obstacle to growth.

The animal then has plenty of room to grow inside the new shell simply by displacing the water.