Two new species belonging to the family Goneplacidae MacLeay, 1838 (Crustacea, Decapoda, Brachyura) are described from the western Pacific Ocean. The first belongs to Carcinoplax H. Milne Edwards, 1852, the second to Pycnoplax Castro, 2007. The new species of Carcinoplax is distinguished from the 18 known species of the genus by the morphologies of the first male pleopods and outer orbital and anterolateral teeth; the new species of Pycnoplax is distinguished from the five known species of the genus by the morphology of the first and second male pleopods and the granular carapace. A female specimen of a third goneplacid, Thyraplax truncata Castro, 2007, which was previously known only from male specimens, is also described. The characters of the two new species further confirm that in the Goneplacidae s.s. the morphology of the external reproductive structures rather than that of the carapace are far more reliable in showing phylogenetic relationships among supraspecific taxa.
Crustacea, Decapoda, Brachyura, Goneplacidae, western Pacific Ocean, new species.