A new family for Sotoplax robertsi Guinot, 1984, with a diagnosis and key to the Goneplacoidea Macleay, 1838 (Crustacea: Decapoda: Brachyura)

Sotoplacidae nov. fam. is described for Sotoplax robertsi Guinot, 1984, a goneplacoid crab from the western Atlantic that had been provisionally placed in the family Euryplacidae Stimpson, 1871. Sotoplax is characterised by a suite of characters, particularly related to the thoracic sternum, male abdomen, and to the protection of the penis, which places it as a taxon independent from the Euryplacidae and the other 10 families currently grouped in the superfamily Goneplacoidea MacLeay, 1838. A diagnosis of the Goneplacoidea, a detailed table of characters diagnostic to the 11 goneplacoid families, and a key to these families are also given.