The large, reddish brown to dark purple kelp crab is often found underneath ledges and in the surf grass at the lowest extent of the low-tide zone. It is primarily a vegetarian or scavenger. The carapace (dorsal shell) is pear-shaped and possesses a few dull tubercles on its margin. The carapace is also projected anteriorly to form a prominent rostrum. A related species, the northern kelp crab, is also found in the same habitat. It can be distinguished by the more elongate, sharper tubercles on the body margin.