Taken primarily from Kozloff, 1987, 1996 p. 411 (Copyright 1987, 1996, University of Washington Press. Used in this web page by permission of University of Washington Press)
An alternate key to a similar group of families can be
found in Wicksten,
2009 page 288.
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| Lower taxonomic level | Main Page | Alphabetic Index | Systematic Index | Glossary |
| 1a | Aggregate of mouthparts tapering anteriorly, thus forming a triangle (carapace broader than long, and with a large, laterally directed tooth originating at the widest part) | Family Calappidae |
| 1b | Aggregate of mouthparts not tapering anteriorly | 2 |
| 2a | With a prominent rostrum that is divided into 2 processes (photo) (these may be partly or wholly fused) | Family Majidae |
| 2b | Without a rostrum (photo) (photo) | 3 |
| 3a | Anterior margin of carapace, between the eyes, usually toothed (not toothed, however, in the family Xanthidae); lateral margins of carapace distinctly toothed (photo) | 4 |
| 3b | Anterior margin of carapace, between the eyes, not toothed; lateral margins of carapace either toothed or not toothed | 6 |
| 4a | Anterior margin of carapace, between the eyes, without teeth, but generally with a slight notch; anterolateral margins of carapace with 3 or more blunt teeth; abdomen of male with 4 segments plus telson | Family Xanthidae |
| 4b | Anterior margin of carapace, between the eyes, with several distinct teeth; anterolateral margins of carapace with at least 6 teeth; abdomen of male with 6 segments plus telson | 5 |
| 5a | Carapace more or less five-angled; marginal teeth with several spines; setae stiff, club-shaped | Family Atelecyclidae:
Telmessus cheiragonus |
| 5b | Carapace broadly oval; each marginal tooth with not more than 1 spine; setae, when present, not club-shaped. [5 carapace teeth between the eyes] | Family Cancridae |
| 6a | Carapace almost rectangular, with distinct teeth on the lateral margins; free-living | Family Grapsidae |
| 6b | Carapace oval or nearly circular, without teeth on the lateral margins; closely associated with other invertebrates (living in worm tubes, ascidians, mantle cavity of bivalve molluscs, etc.) | Family Pinnotheridae |