【Prefecturally Designated：Natural Monument (Fauna)】Miyako Sawa-Gani (Geothelphusa miyakoensis)

The Miyako Sawa-Gani is a native freshwater crab of Miyako Island. It has a carapace width of about 3cm, and is said to be closely related to the Osawa-Gani crabs of Tokashiki Island. It is mostly active underwater, and is nocturnal, feeding on land snails and organic matters in the water. The freshwater crab species only inhabit inland waters or on land where they spend their whole lives, and are not able to live in seawater.
The generally accepted theory of Miyako Island is that it was once submerged in the seas and later on, it never connected with other land; this species of freshwater crab is an important factor in re-examining the geologic history of Miyako Island and of the Ryukyu Archipelago.
It has a limited habitat and is an endangered species.