Species information
Scientific name: Geothelphusa sakamotoanus
Japanese name: サカモトサワガニ
Chinese name: 坂本澤蟹
English name: Sakamoto Freshwater Crab
Origin: Okinawajima, Amami Oshima, Tokunoshima, Kikaijima
Ecology and description
Sakamoto Freshwater Crab is distributed not only in the northern part of Okinawajima but also in its central and southern regions. It is also found on Amami Oshima, Tokunoshima, and Kikaijima, making it the most widely distributed freshwater crab species in the Ryukyu Islands.
The crab guide booklet for the Amami Islands mentions that Sakamoto Freshwater Crab exhibits a wide range of body colors, from deep red to light yellow and blue-gray. A characteristic feature is the serrated projection on the edges of the carapace, which is approximately 4 cm in width and glossy.
In my observations, I find that the appearance of individuals from Okinawajima differs from those on Tokunoshima and Amami Oshima. The population on Okinawajima is almost uniformly yellow-brown in color, smaller in size compared to those on Tokunoshima and Amami Oshima, and the carapace is less glossy. Further taxonomic research may be needed.
I am very curious about the origin of Sakamoto Freshwater Crab’s name, specifically which Sakamoto it is named after. Who was Mr. F. Sakamoto, the collector mentioned in the 1904 published paper?
Rathbun, M. J., 1904. Les crabes d’eau douce (Potarnonidae). Nouv. Arch. Mus. Hist. Nat. Paris, ser. IV, 6 : 206.
Field photographs taken during our tours, with observation dates
During our 【Herping】 tour in the summer season, we sometimes encounter this species when visiting stream environments.
