Geothelphusa grandiovata
Japanese name: オキナワオオサワガニ
Chinese name: 巨圓澤蟹
English name: Okinawa Geothelphusa Freshwater Crab
Origin: Endemic to Okinawajima
Geothelphusa grandiovata is the largest species of Geothelphusa freshwater crabs found in Japan. Its carapace is smooth and glossy, and coloration varies widely from reddish brown to yellowish brown and purplish brown. The species name grandiovata is a combination of “grandis” (large) and “ovatus” (oval), reflecting its large size and strongly arched carapace.
In the past, populations from Tokashikijima, Kumejima, and Iheya Island were considered the same species. However, detailed studies revealed that populations on nearly every island have diverged into separate species. This species is now recognized as endemic to Okinawajima.
The life cycle of this crab takes place entirely in mountain streams. Females carry their eggs under the abdomen and protect the young until they complete their first molt. This species is omnivorous and has been observed feeding on frogs, acorns from Fagaceae trees, and snails.
Other notes:
A yellow individual was discovered in Yambaru, surprising even the guide! (News report on 2022/4/26)