Geothelphusa tenuimanus
Japanese name: ヒメユリサワガニ
Chinese name: 細掌澤蟹
English name: Himeyuri Freshwater Crab
Origin: Endemic to Okinawajima
The Himeyuri Freshwater Crab is a relatively small species with a carapace width of about 3 cm. It is characterized by extremely slender walking legs and a body color that is usually tinged with purplish-red. It inhabits limestone areas on Okinawajima, and its populations are fragmented and limited to isolated areas in the north, central, and south parts of the island. The species is typically found in moderately moist environments such as trees and caves in limestone habitats, but local populations are generally small.
Like other Geothelphusa species, Geothelphusa tenuimanus does not release its eggs into the sea. Instead, the female cares for the eggs until the young crabs molt for the first time. In the case of Geothelphusa tenuimanus, the eggs are about 4–5 mm in diameter and number only around 25, making them the largest and fewest among Japanese Geothelphusa species. The hatchlings are also relatively large. While most freshwater crabs release their juveniles into the water, this species deposits them directly on land, indicating a high level of terrestrial adaptation.
This species is considered one of the most terrestrial-adapted freshwater crabs in East Asia and is a unique and valuable example from an evolutionary perspective. In addition, fossils of this species have been discovered, adding to its academic significance.
The species name tenuimanus is derived from the Latin tenui (slender) and manus (hand), referring to its slender legs. The Japanese name “Himeyuri” evokes the memory of the “Himeyuri Student Corps,” a group of local schoolgirls who served and died during World War II. While there is a monument dedicated to them in southern Okinawajima, The original species description paper does not specify whether the name was chosen with this reference in mind.
Naruse, T., Karasawa, H., Shokita, S., Tanaka, T. & Moriguchi, M. (2003).
A first fossil record of the terrestrial crab, Geothelphusa tenuimanus (Miyake & Minei, 1965) (Decapoda, Brachyura, Potamidae) from Okinawa Island, Central Ryukyus, Japan. Crustaceana, 76(10), 1211–1218. https://doi.org/10.1163/156854003773123521
