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Biology/Natural History: This species is said to feed by scooping up sediment with its claws, and also to feed on the clams it digs up. Will Duguid reports that in the laboratory adults of this species are strongly attracted to and feeds on brittle stars. They may also feed on urchins such as Strongylocentrotus droebachiensis. It is thought that octopus may be its main predator. It may bury itself in the sediment, except that the front with the foramen is exposed for breathing. The abdomen has knobby plates and Flora and Fairbanks say it is also partly soft and not held very tightly against the thorax (this seems to conflict with other accounts). An intrmittent open coast fishery for this species exists off Oregon. This species is said to occur in large aggregations of mixed males and females on soft bottoms. Molting within an aggregation seems to be synchronous, but not synchronized with that of other aggregations. Eggs and larvae of snailfish, especially Careproctus melanurus, the blacktail snailfish, are often found among the gill filaments of these crabs. These may occur in large numbers and even may contribute to collapse of the gills, but usually they do not seem to cause any harm.
Off British Columbia this species has a biennial (two-year) cycle for brooding. Females molt and breed during mid-summer, then brooded their eggs and larvae for 18 months before releasing them as zoeae the second winter or early spring (Feb-April) after breeding. Much of this long brooding period was due to the fact that the brooded eggs underwent a 12-month diapause in the gastrula stage. The females released the larvae gradually, averaging a period of 69 days. Brooding females have a mean carapace length of 8.9 cm (width 10.7 cm) and a minimum carapace length of 7.5 cm (width 8.8 cm). Females which have been brooding for a number of months and post-breeding females often have extensive overgrowth of polychaete tubeworms, hydrozoans, and small bivalves. The distal legs and much of the underside has a black stain not seen on males or pre-incubation females (Duguid and Page, 2011).