[2] Both of these eastern Pacific crab species are recognized by ITIS as belonging to the much larger genus Cancer.

Female crabs can be distinguished from males by a broad tail flap on their undersides, which are used for protecting their eggs when they are gravid.

M. gracilis only grows to a width of about 3.5 inches (9 cm) and resembles a juvenile M. magister (Dungeness Crab).

More obscure ways to tell are by the appearance of hair on the posterior three legs of M. magister where M. gracilis is almost always hairless.

Another telling characteristic of the slender crab is that the last segment of its tail flap is pointed, where M. magister is curved.