Redefinition and revision of Ser Rathbun, 1931 (Decapoda: Brachyura: Pilumnidae)

The taxonomy of the setose brachyuran crabs Ser fukiensisRathbun, 1931 and Litocheira amoyensisGordon, 1930, both described based on material from Fujian, China, have been poorly understood for decades.. The monotypic genus SerRathbun, 1931 had been placed under Carcinoplacinae H. Milne Edwards, 1852 and Rhizopinae Stimpson, 1858 by subsequent authors. Examining type lots of both species and recently acquired material, we find the holotype of L. amoyensis is an immature male but this name represents a senior synonym of Ser fukiensis. The genus Ser is re-diagnosed and hereby placed under Pilumninae Samouelle, 1819. It is here considered to contain three species: the type species, Ser fukiensis (= S. amoyensiscomb. nov.); S. sasekumari (Serène, 1971) comb. nov.; and S. mikawaensis (Sakai, 1969) comb. nov.. Comparisons are made between Ser and morphologically similar genera: RhizopoidesNg, 1987, CryptocoelomaMiers, 1884, PseudolitochiraWard, 1942, BossacarcinusŠtevčić, 2011, and HeteropilumnusDe Man, 1895. It is also apparent that Heteropilumnus is a morphologically heterogeneous group, and that its type species, H. stormiDe Man, 1895, is quite distinct from other species currently included in the genus. We discuss the implications of this finding, especially as it pertains to Ser.