Two species of Ceradocus collected from coastal areas in Japan, with description of a new species (Crustacea: Amphipoda: Maeridae).

Two species of the amphipod genus Ceradocus Costa, 1853 were collected from coastal areas in Japan: C. kiiensis sp. nov. from Wakayama Prefecture and C. laevis Oleröd, 1970 from Okinawa Prefecture. Both of the species share the asymmetrical male gnathopod 2, the larger male gnathopod 2 with strongly oblique palm and the uropod 3 with wide rami. Ceradocus kiiensis also has the palm with a single excavation in the larger male gnathopod 2 and the pleonites 1-3 with many dorsal teeth. This new species can be distinguished from its congeners by the absence of the anterodistal projection on the basis of the larger male gnathopod 2, the presence of the posterior teeth on the pleonal epimera 1-2, and others. Ceradocus laevis is characterized by the palm having triangular and small trapezoidal projections in the larger male gnathopod 2, the pereopods 5-7 bases with rounded posterodistal lobe, the pleonites and urosomites lacking dorsal teeth, and the pleonal epimera 1-2 without posterior teeth. This species can be easily distinguished from C. kiiensis by the smooth dorsal margins of the pleonites. A key to Ceradocus species in Japan is provided.