Taken primarily from Kozloff, 1987, 1996 (Copyright 1987, 1996, University of Washington Press. Used in this web page by permission of University of Washington Press)
An excellent alternate, up to date key can be found on
page 387 of Wicksten,
2009.
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| Lower taxonomic level | Main Page | Alphabetic Index | Systematic Index | Glossary |
| 1a | Merus of legs 2-5 much flattened, used for swimming; male without a tuft of hairs on the propodus of the cheliped; oceanic crabs, only occasionally washed onto shore with floating debris or other animals | 2 |
| 1b | Merus of legs 2-5 not markedly flattened; male with a tuft of hairs on the propodus of the cheliped; common intertidal crabs | 3 |
| 2a | Carapace decidedly longer than wide; lateral margins convex | Planes cyaneus |
| 2b | Carapace only slightly longer than wide; lateral margins almost straight, but converging slightly posteriorly | Planes marinus |
| 3a | Dorsal surface of carapace with flat transverse ridges, and with red or purple transverse lines on a blackish green background; carapace with 2 teeth on the anterolateral margin (not likely to be found north of Oregon) | Pachygrapsus crassipes |
| 3b | Dorsal surface of carapace without flat transverse ridges and without transverse lines; carapace with 3 teeth on the anterolateral margin | 4 |
| 4a | Legs fringed with abundant hairs (photo); prevailing coloration generally grayish green; chelipeds without conspicuous purple spots (photo) | Hemigrapsus oregonensis |
| 4b | Legs not obviously hairy; prevailing coloration generally reddish; chelipeds with conspicuous purple spots | Hemigrapsus nudus |