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 ten exclusively fossil genera, in two subfamilies:
The Grapsoidea are a superfamily of crabs; they are well known and contain many taxa which are terrestrial (land-living), semiterrestrial, or limnic. Another well-known member with a more conventional lifestyle is the Chinese mitten crab, Eriocheir sinensis.
Xanthoidea is a superfamily of crabs, comprising seven families. 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. Montezumellidae has been moved from Cancroidea to his own Superfamily Montezumelloidea Ossó & Domínguez, 2019.
Gecarcinucoidea is a superfamily of freshwater crabs. Its members have been grouped into families in various ways, with some authors recognizing families such as "Deckeniidae", "Sundathelphusidae", and "Parathelphusidae", but now only the family Gecarcinucidae is currently recognized.
Goneplacidae is a family of crabs of the order Decapoda and the superfamily Goneplacoidea. It includes the following genera:
Hexapodidae is a family of crabs, the only family in the superfamily Hexapodoidea. It has traditionally been treated as a subfamily of the family Goneplacidae, and was originally described as a subfamily of Pinnotheridae. Its members can be distinguished from all other true crabs by the reduction of the thorax, such that only seven sternites are exposed, and only four pairs of pereiopods are present. Not counting the enlarged pair of claws, this leaves only six walking legs, from which the type genus Hexapus, and therefore the whole family, takes its name. Some anomuran "crabs", such as porcelain crabs and king crabs also have only four visible pairs of legs. With the exception of Stevea williamsi, from Mexico, all the extant members are found either in the Indo-Pacific oceans, or around the coast of Africa.
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.
Epialtidae is a family of crabs, containing the subfamilies:
Hepatella amica is a genus of crabs in the family Aethridae. It is the only species in the genus Hepatella.
Ashtoret is a genus of crabs in the family Matutidae, containing the following species:
Zosimus is a genus of crabs in the family Xanthidae, containing the following species:
Around 65 species of crab occur in the waters of the British Isles. All are marine, with the exception of the introduced Chinese mitten crab, Eriocheir sinensis, which occurs in fresh and brackish water. They range in size from the deep-water species Paromola cuvieri, which can reach a claw span of 1.2 metres, to the pea crab, which is only 4 mm (0.16 in) wide and lives inside mussel shells.
Mathildellidae is family of crabs belonging to the superfamily Goneplacoidea, containing the following genera:
Dynomenidae is a family of crabs in the superfamily Dromioidea mostly found in Madagascar. There are nineteen genera in this family: five extant and fourteen known from fossils:
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.
