Portunus is a genus of crab which includes several important species for fisheries, such as the blue swimming crab, Portunus pelagicus and the Gazami crab, P. trituberculatus. Other species, such as the three-spotted crab (P. sanguinolentus) are caught as bycatch.
Atelecyclus rotundatus is a medium-sized crab found on the west coast of Europe and Africa as well as almost all the Mediterranean Sea and on the Cape Verde and Canary islands. It has many common names, including circular crab, round crab and old man's face crab. It measures about 40 millimetres (1.6 in) across its almost circular, reddish-brown carapace and lives on coarse soft bottoms at shallow depths. There are 9–11 sharp teeth on the front and 3 teeth between the eyes.
The Ocypodidae are a family of semiterrestrial crabs that includes the ghost crabs and fiddler crabs. They are found on tropical and temperate shorelines around the world.
The Grapsidae are a family of crabs known variously as marsh crabs, shore crabs, or talon crabs. The family has not been confirmed to form a monophyletic group and some taxa may belong in other families. They are found along the shore among rocks, in estuaries, marshes, and in some cases pelagic among drifting seaweeds and flotsam.
Cancridae is a family of crabs. It comprises six extant genera, and eleven exclusively fossil genera, in two subfamilies:
Xanthoidea is a superfamily of crabs, comprising the three families Xanthidae, Panopeidae and Pseudorhombilidae. Formerly, a number of other families were included in Xanthoidea, but many of these have since been removed to other superfamilies. These include Carpilioidea, Eriphioidea, Hexapodoidea, Pilumnoidea and Trapezioidea. Even in this reduced state, Xanthoidea remains one of the most species-rich superfamilies of crabs.
Cancroidea is a superfamily of crabs, comprising the families Atelecyclidae and Cancridae. Four other families have been separated into new superfamilies: Cheiragonidae into Cheiragonoidea, Corystidae into Corystoidea, and both Pirimelidae and Thiidae into Portunoidea.
Parathelphusinae is a subfamily of freshwater crabs, which was formerly placed in the family Parathelphusidae; they are mainly found in South and Southeast Asia, but also found elsewhere in Asia and in Australia. The family is now considered as a junior synonym of the family Gecarcinucidae.
The Sesarmidae are a family of crabs, previously included in the Grapsidae by many authors. Several species, namely in Geosesarma, Metopaulias, and Sesarma, are true terrestrial crabs. They do not need to return to the sea even for breeding.
Goneplacidae is a family of crabs of the order Decapoda and the superfamily Goneplacoidea. It includes the following genera:
Cheiragonidae is a small family of crabs, sometimes called helmet crabs, placed in its own superfamily, Cheriagonoidea. It comprises three extant species, Erimacrus isenbeckii, Telmessus acutidens and Telmessus cheiragonus, there are no yet evidences of Cheiragonidae in the fossil record. Many of these crabs were formerly treated as members of the Atelecyclidae.
Matutidae is a family of crabs, sometimes called moon crabs, adapted for swimming or digging. They differ from the swimming crabs of the family Portunidae in that all five pairs of legs are flattened, rather than just the last pair, as in Portunidae. Crabs in the Matutidae are aggressive predators.
Pseudozioidea is a superfamily of crabs, formerly treated in the Eriphioidea, Carpilioidea, Xanthoidea, Pilumnoidea and Goneplacoidea. A number of fossils from the Eocene onwards are known from the family Pseudoziidae. Eleven genera are recognised in three families:
Palicoidea is a superfamily of crabs, comprising the two families Crossotonotidae and Palicidae. Together, they contain 13 genera, including two genera in the Palicidae known only from fossils. The two families were previously treated as two subfamilies in a Palicidae of wider circumscription.
Epialtidae is a family of crabs, containing the subfamilies:
Xantho is a genus of crabs in the family Xanthidae, containing five extant species, all restricted to the north-east Atlantic Ocean and Mediterranean Sea, although Xantho granulicarpis is not universally recognised as a separate species from Xantho hydrophilus:
Mathildellidae is family of crabs belonging to the superfamily Goneplacoidea, containing the following genera:
Ethusidae is one of two extant families of crabs in the superfamily Dorippoidea. It contains four genera. Members of this family are found in marine environments at depths from 16m to 4,192m.
Galene is a genus of crabs belonging to the family Galenidae
Necrocarcinidae is an extinct family of Cretaceous crabs. It comprises 40 species grouped in seven genera.
