Geothelphusa sakamotoanus
Japanese Name: サカモトサワガニ
Chinese Name: 坂本澤蟹
English Name: Sakamoto Freshwater Crab
Origin: Okinawa Island, Amami Oshima, Tokunoshima, Kikai Island
The Sakamoto Freshwater Crab is widely distributed in the Ryukyu Islands, including both the northern and central-southern regions of Okinawa Island, as well as on Amami Oshima, Tokunoshima, and Kikai Island. Among the freshwater crabs in the Ryukyu archipelago, this species has the broadest range.
According to the Amami island’s Freshwater Crab guidebook, the Sakamoto Freshwater Crab exhibits a variety of colors, from deep red and light yellow to blue-gray. It is characterized by serrated protrusions along the front edge of the carapace, which measures about 4 cm and has a glossy appearance.
Observations suggest that the Okinawa Island population appears different in appearance compared to those from Tokunoshima and Amami Oshima. The crabs on Okinawa Island are mostly yellow-brown, smaller in size, and with a less glossy carapace. Further taxonomic research may be needed to clarify these regional differences.
I am very curious about the origin of the Sakamoto name—specifically, who was “Mr. F. Sakamoto” mentioned as a collector in the 1904 paper by Rathbun?
Rathbun, M. J., 1904. Les crabes d’eau douce (Potarnonidae). Nouv. Arch. Mus. Hist. Nat. Paris, ser. IV, 6 : 206.
